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HVAC Heat Not Working? Try These Solutions Before Paying for Repair [2025]

by

When your heating system stops working during cold weather, it’s more than just uncomfortable – it can be dangerous, especially for young children, elderly family members, and pets. Frozen pipes, property damage, and health risks make a non-functioning furnace or heat pump a genuine emergency that requires immediate attention.

This comprehensive guide will help you diagnose why your HVAC heat isn’t working and provide proven solutions to restore warmth to your home, potentially saving you hundreds of dollars in emergency service calls while keeping your family safe and comfortable.

Understanding Your Heating System

Before troubleshooting, it helps to understand what type of system you have:

Forced Air Furnace (Most Common):

  • Gas furnace: Burns natural gas or propane
  • Electric furnace: Uses heating elements (like giant toaster)
  • Oil furnace: Burns heating oil (less common, mostly Northeast)
  • All use blower to distribute warm air through ductwork

Heat Pump:

  • Reverses AC process to extract heat from outdoor air
  • Electric backup heat (heat strips) for extreme cold
  • More efficient than electric furnace in moderate climates
  • Struggles in temperatures below 25-30°F

Boiler System:

  • Heats water or creates steam
  • Distributes through radiators or baseboard heaters
  • No forced air or ductwork
  • Common in older homes

Ductless Mini-Split:

  • Individual units mounted on walls
  • Heat pump technology
  • No ductwork needed
  • Each room controlled independently

How Forced Air Heating Works:

  1. Thermostat calls for heat
  2. Gas valve opens (gas furnace) or heating elements energize (electric)
  3. Burner ignites or elements heat up
  4. Heat exchanger warms air
  5. Blower circulates warm air through ducts
  6. System cycles until desired temperature reached

Understanding your system type helps target troubleshooting efforts.

Quick Diagnostic Checks

Before calling for service, try these simple tests:

Check Thermostat:

  • Is it set to “Heat” mode (not “Cool” or “Off”)?
  • Is temperature set above current room temperature?
  • Is display lit/showing information?
  • Are batteries fresh (if battery-powered)?

Check Power:

  • Is furnace/air handler getting power?
  • Check circuit breakers—often two breakers for HVAC
  • Look for emergency shutoff switch (looks like light switch)
  • Verify all switches in “On” position

Listen and Look:

  • Does furnace make any sound when heat called?
  • Does blower motor run?
  • Can you hear ignition clicking?
  • Any unusual sounds (banging, squealing, rumbling)?

Visual Inspection:

  • Flame visible through viewing window (gas furnace)?
  • Error codes on control board?
  • Standing water around unit?
  • Visible damage to components?

These quick checks often reveal obvious problems with simple solutions.

Common Causes and Solutions

1. Thermostat Issues

The thermostat is the command center for your heating system.

Symptoms:

  • Heat doesn’t turn on at all
  • Runs constantly without reaching temperature
  • Turns on and off too frequently
  • Display blank or dim
  • Wrong temperature readings

Common Thermostat Problems:

Dead or Weak Batteries:

  • Battery-powered thermostats need fresh batteries
  • Low batteries cause erratic behavior or complete failure
  • Display may be dim, blank, or showing low battery icon
  • Replace every 6-12 months preventively

Solution:

  1. Open thermostat cover or remove from wall plate
  2. Remove old batteries
  3. Install fresh batteries (check polarity)
  4. Wait for display to activate (may take 30 seconds)
  5. Reset time/date if necessary
  6. Verify mode set to “Heat”
  7. Test heat operation

Wrong Mode Setting:

  • Set to “Cool” or “Off” instead of “Heat”
  • Fan set to “On” (runs constantly) instead of “Auto”
  • Common after someone adjusts controls

Solution:

  1. Check mode switch or setting
  2. Set to “Heat”
  3. Set fan to “Auto” (blower runs only when heating)
  4. Set temperature 5°F above current room temperature
  5. Wait 3-5 minutes for system to respond

Temperature Set Too Low:

  • Set at or below current room temperature
  • System won’t call for heat
  • Easy oversight when making adjustments

Solution:

  • Raise set temperature to at least 5°F above room temperature
  • Wait 5 minutes for system to start
  • Adjust to comfortable setting once heating confirmed

Dirty Temperature Sensor:

  • Dust accumulation affects accuracy
  • Thermostat reads incorrectly
  • May not call for heat when needed

Solution:

  1. Remove thermostat cover or body from wall plate
  2. Gently blow dust away with compressed air
  3. Use soft brush to clean sensor (small bead or coil visible inside)
  4. Don’t touch sensor directly (skin oils affect readings)
  5. Ensure sensor doesn’t touch back wall
  6. Reinstall and test

Loose or Corroded Wiring:

  • Wires disconnected from terminals
  • Corrosion on wire ends or terminals
  • Pet or rodent damage to low-voltage wiring

Solution:

  1. TURN OFF POWER at breaker before touching wires
  2. Remove thermostat from wall plate
  3. Check all wire connections at terminals
  4. Look for loose screws or pulled-out wires
  5. Check for corrosion (green/white buildup)
  6. Clean terminals with fine sandpaper if corroded
  7. Ensure each wire firmly seated in correct terminal
  8. Tighten terminal screws
  9. Reattach thermostat and restore power
  10. Test operation

Common Wire Color Code:

  • R or Rc: 24V power (red)
  • W or W1: Heat call (white)
  • G: Blower/fan (green)
  • Y or Y1: Cooling call (yellow)
  • C: Common/return (blue or black)
  • Take photo before disconnecting any wires

Thermostat Location Issues:

  • In direct sunlight (reads warmer than actual)
  • Near heat sources (fireplace, lamps, kitchen)
  • In drafty area or near exterior door
  • Reads temperature incorrectly due to poor placement

Temporary Solution:

  • Shade from direct sunlight
  • Keep heat sources away
  • Close nearby drafts

Permanent Solution:

  • Relocate thermostat to interior wall
  • Central location in home
  • About 5 feet above floor
  • Away from vents, direct sun, drafts
  • Professional relocation: $150-300

Smart Thermostat Issues:

  • WiFi disconnected
  • App not communicating with thermostat
  • Lost C-wire power
  • Software glitch

Solution:

  1. Check WiFi connection in thermostat settings
  2. Reboot thermostat (power cycle or menu option)
  3. Verify C-wire connected (common wire for continuous power)
  4. Update thermostat firmware through app
  5. Delete and re-add thermostat in app if necessary
  6. Reset to factory settings as last resort

Schedule Override:

  • Programmed schedule keeping temperature low
  • Away mode or vacation hold active
  • Energy-saving settings too aggressive

Solution:

  1. Check current schedule in thermostat
  2. Verify no hold or override active
  3. Disable away mode if activated
  4. Adjust schedule if too low during desired heating times
  5. Use manual override: set to “Hold” at desired temperature

2. Power Supply Problems

No power means no heat—check all power sources.

Tripped Circuit Breaker:

Why Breakers Trip:

  • Electrical overload
  • Short circuit in system
  • Blower motor drawing too much current
  • Ground fault
  • Age-related breaker failure

Solution:

  1. Locate main electrical panel
  2. Find HVAC breakers (typically labeled “Furnace” or “HVAC”)
  3. Most systems have two breakers:
    • One for furnace (120V or 240V)
    • One for air handler/blower (120V)
  4. Look for breaker in tripped position (handle in middle, not fully “On” or “Off”)
  5. Turn breaker completely “Off” first
  6. Then flip firmly to “On”
  7. Listen for furnace to power up (usually clicks or hums)
  8. Wait 5 minutes before testing heat
  9. If trips again immediately: STOP—Call professional

CRITICAL: Repeatedly tripping breaker indicates serious electrical problem. Do not keep resetting—fire hazard.

Emergency Shutoff Switch:

  • Looks like standard light switch
  • Usually red or has red plate
  • Located at or near furnace
  • Required by code for safety
  • Commonly turned off accidentally

Common Locations:

  • On wall near furnace
  • At top of basement stairs
  • On furnace cabinet itself
  • Near air handler in attic

Solution:

  1. Locate emergency switch
  2. Verify in “On” position (up)
  3. May be labeled “Emergency Shutoff,” “Furnace,” or “HVAC”
  4. Test heat after confirming switch on

Furnace Door Switch:

  • Safety interlock prevents operation with door open
  • Small button or lever inside door frame
  • Door not fully closed or latched
  • Switch can fail or stick

Solution:

  1. Check furnace access panel fully closed
  2. Should fit flush and click into place
  3. Look for small button or switch being depressed by door
  4. Clean any debris around door frame
  5. If door won’t stay closed, check latches or clips
  6. Replace broken door switch ($10-30 part)

Blown Fuse:

  • 3-5 amp fuse on control board (inside furnace)
  • Purple/violet fuse common in modern furnaces
  • Protects low-voltage control circuit
  • Located on or near control board

Solution:

  1. Turn off power at breaker
  2. Remove furnace access panel
  3. Locate control board (circuit board with colored wires)
  4. Find small automotive-style fuse (usually purple)
  5. Remove fuse and inspect:
    • Clear window: Fuse good
    • Cloudy or broken filament: Fuse blown
  6. Replace with exact same amperage (usually 3A or 5A)
  7. NEVER use higher amperage—fire hazard
  8. If fuse blows again immediately, indicates short circuit—call professional

Transformer Failure:

  • Steps down 120V to 24V for thermostat circuit
  • Can burn out from power surges or age
  • Small rectangular box with wires on furnace
  • May hum or be hot to touch if failing

Test Transformer:

  1. Turn off power at breaker
  2. Remove furnace panel
  3. Locate transformer (usually has two wires going to thermostat)
  4. Use multimeter on AC voltage setting
  5. Turn power back on
  6. Measure across 24V terminals (should read 24-28V)
  7. If no voltage, transformer failed
  8. Replacement: $50-150 professional install

Power Outage or Surge:

  • Recent power outage may have tripped safety controls
  • Surge may have damaged control board
  • System may need manual reset

Solution:

  1. Turn off power at breaker
  2. Wait 5 full minutes (allows reset of safety controls)
  3. Restore power
  4. System should go through startup sequence
  5. If repeatedly fails after power outage, may have surge damage
  6. Check control board for burned components or LED error codes

3. Dirty Air Filter

Restricted airflow is the most common cause of heating problems.

Why Filters Are Critical:

  • Furnace needs proper airflow to operate safely
  • Dirty filter restricts air movement
  • Causes overheating (furnace shuts down)
  • Reduces heating efficiency
  • Can crack heat exchanger (expensive damage)
  • Increases energy bills 15-30%

Symptoms:

  • Heat runs briefly then shuts off
  • Weak airflow from vents
  • Furnace cycles on and off frequently
  • Takes long time to heat house
  • Blower runs but little heat produced
  • Burning smell from vents

How Dirty Filter Causes Shutdown:

  • Restricted airflow = heat exchanger gets too hot
  • High-limit switch detects excessive temperature
  • Shuts off burner to prevent damage
  • Blower continues running to cool system
  • Cycle repeats, house doesn’t heat

Filter Replacement Schedule:

  • Standard 1-inch fiberglass filters: Every 1 month
  • Pleated 1-inch filters: Every 1-2 months during heating season
  • 4-inch thick filters: Every 6 months
  • Homes with pets: More frequently
  • Dusty environments: Check monthly
  • During heavy use (winter): Check monthly minimum

Solution:

Locate Air Filter:

  • Usually in return air vent (large grille on wall or ceiling)
  • Or at furnace/air handler
  • May be horizontal or vertical slot
  • Should be accessible without tools in most systems

Inspect Filter:

  1. Turn off system at thermostat (not required but safer)
  2. Remove filter from slot
  3. Hold up to light:
    • Can see light through clearly: Okay but check date
    • Light barely penetrates: Needs replacement soon
    • Cannot see light at all: REPLACE IMMEDIATELY
  4. Note size printed on filter frame (e.g., 20x25x1, 16x20x1)
  5. Check arrow on frame (shows airflow direction)

Replace Filter:

  1. Remove old filter
  2. Purchase exact same size replacement
  3. Note arrow on new filter frame (toward furnace/ductwork)
  4. Insert new filter:
    • Arrow points toward furnace (away from return)
    • Should fit snugly in slot
    • No gaps for air to bypass
  5. Turn system back on
  6. Check airflow at vents (should improve within minutes)

Temporary Solution if No Replacement Available:

  • Remove filter completely (better than clogged filter)
  • Furnace can run briefly without filter (emergency only)
  • Order/buy replacement immediately
  • Don’t run more than 1-2 days without filter (dust damages system)

Filter Type Selection:

  • MERV 8: Basic filtration, good airflow, most homes
  • MERV 11: Better filtration, allergy sufferers
  • MERV 13: Excellent filtration, may restrict airflow in older systems
  • Fiberglass: Cheapest but least effective
  • Pleated: Better filtration, lasts longer
  • Electrostatic: Washable, reusable
  • HEPA: Hospital-grade, requires system modification

Important: Don’t exceed system’s recommended MERV rating. Higher ratings restrict airflow more. Check furnace manual or ask HVAC professional.

Preventive Measures:

  • Buy filters in bulk (cheaper and always available)
  • Set phone reminder to check monthly
  • Write date on filter frame when installed
  • Keep spare filters near furnace

4. Pilot Light or Ignition Problems (Gas Furnaces)

Modern furnaces use electronic ignition; older ones have pilot lights.

Standing Pilot Light (Older Furnaces):

Pilot Light Out:

  • Small flame should always be burning
  • Visible through viewing window
  • Blue flame indicates proper combustion
  • Yellow/orange flame indicates problem

Why Pilot Goes Out:

  • Draft blows out flame
  • Thermocouple failure
  • Gas supply interrupted
  • Dirty pilot orifice
  • Low gas pressure

Solution – Relight Pilot:

SAFETY FIRST: If you smell gas, DO NOT attempt to light. Leave house immediately and call gas company or fire department.

Relighting Procedure:

  1. Locate pilot light assembly (check furnace diagram or manual)
  2. Turn gas valve to “Off”
  3. Wait 5 minutes (allows gas to dissipate)
  4. Turn gas valve to “Pilot”
  5. Press and hold pilot button/knob
  6. Use long lighter or match to ignite pilot
  7. Continue holding pilot button for 60 seconds
  8. Release button—pilot should stay lit
  9. If pilot stays lit, turn valve to “On”
  10. If pilot goes out, repeat or call professional

If Pilot Won’t Stay Lit:

  • Thermocouple likely failed (safety device)
  • Needs professional replacement
  • Cost: $100-200
  • Cannot bypass—safety hazard

Electronic Ignition (Modern Furnaces):

Types:

  • Intermittent pilot: Sparks to create pilot when needed
  • Hot surface ignitor: Glows orange to ignite gas
  • Direct spark ignition: Sparks directly at burner

Signs of Ignition Failure:

  • Clicking sound but no ignition
  • No clicking at all
  • Furnace attempts to start repeatedly
  • LED error code on control board (count flashes)

Hot Surface Ignitor Failure (Most Common):

  • Ceramic element glows orange when working
  • Cracks with age (typically 4-7 year life)
  • Visible through viewing window
  • Does not glow = failed ignitor

Solution:

  1. Turn off power at breaker
  2. Remove furnace access panel
  3. Locate ignitor (usually near burners, glows orange)
  4. Look for visible cracks (may need flashlight)
  5. If cracked, needs replacement
  6. DIY: $20-40 for part, fairly straightforward
  7. Professional: $150-250 installed

Flame Sensor Dirty:

  • Metal rod near burners
  • Detects presence of flame
  • Gets coated with carbon/residue
  • Cannot detect flame even though present
  • Shuts down gas as safety measure

Symptoms:

  • Furnace ignites then shuts off after 3-10 seconds
  • Burners light then go out
  • Cycles repeatedly
  • Error code indicates flame sensing failure

Solution – Clean Flame Sensor:

  1. Turn off power at breaker and gas valve
  2. Remove furnace access panel
  3. Locate flame sensor (metal rod, usually in burner area)
  4. Disconnect wire connector
  5. Remove mounting screw (usually 1/4″ hex head)
  6. Remove sensor from bracket
  7. Use fine emery cloth or light sandpaper (400-grit)
  8. Gently polish metal rod until shiny
  9. Do NOT use anything coarse (don’t scratch rod)
  10. Reinstall sensor, reconnect wire
  11. Restore power and gas
  12. Test operation

This simple cleaning fixes many “no heat” calls and costs nothing!

Pressure Switch Problems:

  • Verifies proper draft/venting
  • Ensures safe exhaust
  • Can fail or get stuck
  • Hose to switch can crack or clog

Symptoms:

  • Furnace won’t start at all
  • Draft motor runs but burners don’t light
  • Error code indicates pressure switch issue

Quick Check:

  1. Locate pressure switch (round device with rubber hoses)
  2. Check hoses for cracks or disconnection
  3. Blow through hose to clear blockage
  4. Listen for click when suction applied to switch
  5. If switch doesn’t click or hose damaged, needs replacement
  6. Professional service recommended ($100-250)

5. Limit Switch Tripping

High-limit switch prevents overheating—critical safety device.

How Limit Switch Works:

  • Monitors heat exchanger temperature
  • Shuts off burner if too hot (typically 200°F)
  • Prevents furnace damage or fire
  • Allows blower to continue (cools system)

Symptoms:

  • Furnace starts, runs briefly (30-90 seconds), shuts off
  • Blower continues after burner stops
  • Cycles repeatedly every few minutes
  • House never reaches temperature
  • May smell hot air or see dust burning off

Common Causes:

Dirty Air Filter (Most Common):

  • See “Dirty Air Filter” section above
  • Restricted airflow causes overheating
  • Fix: Replace filter immediately

Blocked Vents or Registers:

  • Too many vents closed
  • Furniture blocking supply vents
  • Return air vents blocked
  • Ductwork disconnected

Solution:

  1. Open all supply vents (registers) at least 75%
  2. Remove any furniture blocking vents
  3. Check that return air vents clear
  4. Ensure all rooms have airflow
  5. Closing too many vents causes overheating
  6. Room doors should be open or have return air path

Dirty Blower Wheel:

  • Dust accumulation on blower fan
  • Reduces airflow significantly
  • Common after years without maintenance

Solution:

  1. Turn off power at breaker
  2. Remove furnace access panel
  3. Locate blower assembly (large fan, squirrel cage design)
  4. Inspect blower wheel blades for dust
  5. Use shop vacuum and brush to clean
  6. May need to remove blower to access thoroughly
  7. Professional cleaning recommended if very dirty

Undersized Ductwork:

  • Ductwork too small for furnace output
  • Causes excessive pressure and heat buildup
  • Design problem requiring professional assessment

Failed Blower Motor:

  • Motor runs slow or not at all
  • Insufficient airflow
  • Causes overheating
  • See “Blower Fan Problems” section

Bad Limit Switch:

  • Switch itself can fail
  • Opens prematurely (before actual overheating)
  • Requires testing with multimeter
  • Professional diagnosis recommended

Solution:

  1. Turn off power
  2. Locate limit switch (disc on furnace plenum)
  3. Use multimeter to test continuity
  4. Should be closed (continuous) when cold
  5. Opens when hot
  6. If open when cold, switch failed
  7. Replacement: $100-200 professional

6. Blower Motor and Fan Issues

Blower circulates heated air—essential for heat delivery.

Symptoms:

  • No air from vents despite furnace running
  • Weak airflow
  • Some vents blow, others don’t
  • Loud squealing, grinding, or humming from furnace
  • Blower runs constantly (won’t shut off)

Common Blower Problems:

Blower Motor Failure:

  • Electric motor burns out over time
  • Bearings seize
  • Overheating from dirty filter
  • Age-related failure (15-20 year typical life)

Signs of Motor Failure:

  • No airflow despite furnace firing
  • Burning smell from furnace
  • Motor hot to touch
  • Humming sound but no rotation
  • Tripped breaker

Solution:

  • Professional replacement required
  • Cost: $300-600 for motor replacement
  • Sometimes entire blower assembly needed: $500-900
  • Consider system age—if over 20 years, may justify replacement vs repair

Blower Belt Broken or Loose (Older Systems):

  • Belt-driven blowers in older furnaces
  • Belt can break, crack, or slip
  • Creates squealing or no blower operation

Solution:

  1. Turn off power at breaker
  2. Remove furnace access panel
  3. Locate belt connecting motor to blower wheel
  4. Inspect for:
    • Cracks or fraying
    • Proper tension (should deflect 1/2″ when pressed)
    • Proper alignment on pulleys
  5. Replace belt if damaged:
    • Note belt number/size
    • Purchase matching belt
    • Install by loosening motor mount
    • Adjust tension (not too tight or too loose)
    • Cost: $15-30 for belt
  6. Professional service: $100-150

Blower Capacitor Failure:

  • Capacitor gives motor starting boost
  • Common failure point (5-10 year life)
  • Prevents motor from starting

Symptoms:

  • Motor hums but doesn’t spin
  • Blower attempts to start but fails
  • Works intermittently
  • Takes long time to start

Solution:

  • Professional replacement recommended
  • Capacitors store electrical charge—dangerous even with power off
  • Cost: $100-250 for replacement
  • DIYers with electrical knowledge can replace (DISCHARGE CAPACITOR FIRST)

Blower Motor Overload:

  • Thermal overload protects motor
  • Shuts off motor if overheating
  • Automatically resets when cool

Causes:

  • Dirty filter restricting airflow
  • Motor running too long continuously
  • Worn motor bearings
  • Electrical problems

Solution:

  1. Turn off system, let cool 30 minutes
  2. Replace air filter
  3. Check for airflow restrictions
  4. Test system after cooling
  5. If repeatedly trips, motor may be failing
  6. Professional diagnosis recommended

Blower Speed Setting Wrong:

  • Multi-speed blowers have adjustable settings
  • Set too low for heating demand
  • Inadequate airflow

Solution:

  1. Check furnace blower speed settings
  2. Usually adjustable at control board or blower motor
  3. Winter setting should be higher than summer
  4. Consult manual for correct speed setting
  5. Professional adjustment recommended if unfamiliar

Blower Won’t Shut Off:

  • Continues running after heat cycle
  • Thermostat fan switch stuck on “On”
  • Fan limit control stuck closed
  • Thermostat or control board failure

Solution:

  1. Check thermostat fan setting (should be “Auto” not “On”)
  2. If set to “On,” fan runs continuously regardless of heat
  3. If set correctly but still runs, likely control board issue
  4. Professional diagnosis needed

7. Gas Supply Problems (Gas Furnaces)

No gas = no heat.

Symptoms:

  • Ignition clicks but no flame
  • Pilot won’t light or stay lit
  • No gas smell at all (good—no leak, but also no supply)
  • Error codes related to ignition failure

Common Gas Supply Issues:

Gas Valve Closed:

  • Manual valve before furnace
  • May be closed accidentally
  • Yellow handle or lever
  • Parallel to pipe = open, perpendicular = closed

Solution:

  1. Locate gas valve (on gas pipe leading to furnace)
  2. Check handle position
  3. Parallel to pipe = open (should be)
  4. Perpendicular (90°) to pipe = closed
  5. Turn to parallel position if closed
  6. Never force—if stuck, call professional

Main Gas Supply Shut Off:

  • Meter valve closed
  • Gas company shut off service
  • Earthquake valve tripped
  • Other appliances also won’t work (gas stove, water heater)

Solution:

  1. Check other gas appliances
  2. If all gas off, check main meter valve
  3. Contact gas utility company
  4. May be non-payment issue or meter problem
  5. After earthquake, automatic shutoff may have triggered
  6. Gas company must restore service—don’t attempt yourself

Empty Propane Tank:

  • For propane systems only
  • Tank runs out
  • Usually have gauge on tank

Solution:

  1. Check propane tank gauge
  2. If empty or very low, schedule delivery
  3. Keep at least 20% full to prevent issues
  4. Set up automatic delivery to prevent running out
  5. After refill, may need to purge air from lines
  6. Professional may need to restart system

Gas Valve Failure:

  • Valve in furnace fails to open
  • Electrical or mechanical failure
  • Requires voltage to open

Testing Gas Valve:

  1. Turn off power
  2. Locate gas valve on furnace
  3. Check electrical connections tight
  4. Turn power back on
  5. When thermostat calls for heat, should hear click from valve
  6. If no click, valve may be bad
  7. Multimeter test: Should have 24V when heating called
  8. Professional replacement recommended: $200-400

Low Gas Pressure:

  • Utility company issue
  • Regulator problem at meter
  • High demand on cold days

Symptoms:

  • Weak or yellow/orange flame
  • Furnace won’t stay running
  • Other gas appliances affected

Solution:

  • Contact gas utility company
  • Cannot adjust pressure yourself
  • May need pressure test at meter
  • Could be community-wide issue during extreme cold

Clogged Gas Orifice or Burners:

  • Dirt, rust, or debris blocks gas flow
  • Prevents proper ignition
  • Reduces heat output

Solution:

  1. Turn off power and gas
  2. Remove burner access panel
  3. Use compressed air to blow out burners
  4. Don’t use wire or tools (can damage orifice)
  5. Look for spider webs, dirt, rust
  6. Professional cleaning recommended for thorough service

8. Vent and Exhaust Problems

Proper venting critical for safety and operation.

High-Efficiency Furnaces (Condensing):

  • PVC vent pipes
  • Intake and exhaust pipes through wall
  • Can freeze or get blocked

Symptoms:

  • Furnace starts then shuts down
  • Error code indicates pressure switch
  • Draft motor runs but burners don’t light
  • Water backing up into furnace
  • Ice on exterior vent pipes

Common Vent Problems:

Blocked Exhaust Vent:

  • Ice buildup on exterior
  • Snow covering vent
  • Bird nest or debris
  • Pipe separated or damaged

Solution:

  1. Go outside and locate vent pipes (usually white PVC)
  2. Check both intake and exhaust clear
  3. Remove any snow, ice, or debris
  4. Ensure pipes angled correctly (slight downward slope away from house)
  5. Check that terminations not blocked
  6. In heavy snow, may need to clear regularly
  7. Install vent guard if recurring issue

Frozen Condensate Line:

  • High-efficiency furnaces produce condensation
  • Drain line can freeze
  • Backs up into furnace
  • Triggers pressure switch

Solution:

  1. Locate condensate drain line
  2. Check for ice blockage
  3. Thaw with warm (not boiling) water
  4. Ensure proper slope for drainage
  5. May need heat tape on exterior portion
  6. Check drain trap not frozen

Damaged or Disconnected Vent Pipe:

  • PVC vent pipes can separate
  • Glue joints fail
  • Pipes crack from age or freezing

Solution:

  1. Inspect entire vent run for damage
  2. Look for gaps at joints
  3. Check for cracks or holes
  4. PVC primer and cement to repair joints
  5. Replace damaged sections
  6. Ensure proper support and slope
  7. Professional repair recommended for safety

Draft Motor Failure:

  • Inducer motor creates draft for venting
  • Pulls exhaust gases out
  • Verifies safe venting before ignition

Symptoms:

  • No sound from furnace when heat called
  • Or motor runs but very noisy
  • Error code indicates draft motor issue

Solution:

  • Professional replacement required
  • Cost: $300-600
  • Critical safety component
  • Cannot bypass

Chimney Problems (Older Furnaces):

  • Blocked chimney
  • Cracked flue
  • Excessive draft
  • Downdraft

Solution:

  • Annual chimney inspection
  • Professional cleaning if needed
  • Chimney cap prevents animals and downdraft
  • Cannot operate without proper draft

9. Heat Pump Specific Issues

Heat pumps have unique problems not found in furnaces.

Understanding Heat Pump Limitations:

  • Extract heat from outdoor air
  • Efficiency drops as temperature falls
  • Struggle below 25-30°F
  • Backup heat (electric strips) expensive to run
  • Defrost cycle normal operation

Heat Pump Not Heating:

Outdoor Unit Not Running:

  • Contactor failure
  • Capacitor failure
  • Reversing valve stuck
  • Low refrigerant

Solution:

  1. Check outdoor unit for power
  2. Verify fan spinning and compressor running
  3. If silent, check breaker and disconnect
  4. If humming but not running, likely capacitor
  5. Professional service needed for compressor/refrigerant issues

Stuck in Defrost Mode:

  • Heat pump periodically defrosts outdoor coil
  • Normal in cold weather
  • Should last 5-15 minutes
  • Stuck in defrost = no heat production

Solution:

  • If defrost runs more than 30 minutes, problem exists
  • Defrost control board or sensor may be bad
  • Professional diagnosis needed
  • Cost: $200-500 depending on issue

Emergency Heat Engaged:

  • Thermostat set to “Emergency Heat” or “E-Heat”
  • Uses expensive backup strips only
  • Bypasses heat pump completely
  • Should only use during heat pump failure

Solution:

  1. Check thermostat mode
  2. Should be set to “Heat” not “Emergency Heat”
  3. “E-Heat” for emergencies only
  4. Higher electric bills result from continuous E-Heat use

Auxiliary Heat Runs Constantly:

  • Backup heat strips supplement heat pump
  • Should only run in extreme cold or when boosting temperature
  • Running constantly indicates problem

Causes:

  • Heat pump not working (strips compensating)
  • Incorrect thermostat settings
  • Refrigerant leak
  • Defrost control problems

Solution:

  • Check heat pump outdoor unit running
  • If outdoor unit off but strips running, heat pump has problem
  • Professional service needed
  • Refrigerant check required

Reversing Valve Stuck:

  • Switches between heating and cooling
  • Can stick in cooling mode
  • Heat pump runs but blows cold air

Symptoms:

  • Cold air from vents when heat called
  • Outdoor unit runs but no heat
  • Works in cooling mode but not heating

Solution:

  • Professional service required
  • Reversing valve replacement: $400-800
  • Or entire outdoor unit if old

Low Refrigerant:

  • Same symptoms as AC low on refrigerant
  • Ice on outdoor coil
  • Reduced heating capacity
  • Higher energy bills

Solution:

  • Professional leak detection and repair
  • System recharge
  • Cannot DIY—requires EPA certification
  • Cost: $200-1,500 depending on leak location

10. Control Board and Electronic Failures

Modern furnaces have sophisticated electronics.

Symptoms:

  • No operation at all
  • Erratic behavior
  • Error codes flashing on LED
  • Some functions work, others don’t

LED Error Codes:

  • Most modern furnaces have diagnostic LED
  • Flashes in patterns indicating specific problems
  • Located on control board inside furnace
  • Count flashes and consult manual or sticker inside furnace

Common Codes:

  • 1 flash: Normal operation
  • 2 flashes: Pressure switch open
  • 3 flashes: Pressure switch stuck closed
  • 4 flashes: Open high-limit switch
  • 5 flashes: Flame sensed when shouldn’t be
  • 6 flashes: No flame sensed when should be
  • 7+ flashes: Various specific errors

Consult furnace manual or manufacturer website for exact code meanings for your model.

Control Board Failure:

  • Age-related failure
  • Power surge damage
  • Water damage
  • Burned components visible

Solution:

  • Professional replacement required
  • Cost: $200-600 for board plus labor
  • Some boards available aftermarket (cheaper)
  • Must match exact model number

Power Surge Damage:

  • Lightning strike nearby
  • Utility surge
  • Can damage control board, transformer, other electronics

Prevention:

  • Whole-house surge protector at panel
  • HVAC-specific surge protector
  • Cost: $200-400 installed
  • Much cheaper than replacing fried control board

Safety Lockout:

  • Multiple failed ignition attempts
  • System shuts down to prevent problems
  • Manual reset usually required

Solution:

  1. Turn off power at breaker
  2. Wait 5 minutes
  3. Restore power (resets system)
  4. If lockout occurs again, indicates real problem
  5. Check for error codes
  6. Call professional if persistent

Heat Not Working: Emergency Measures

If Heat Completely Out in Extreme Cold:

Immediate Actions:

  1. Close off unused rooms – concentrate heat sources in smaller area
  2. Open interior doors – allows any residual heat to circulate
  3. Use alternative heat sources safely:
    • Electric space heaters (only UL-listed, keep away from combustibles)
    • Fireplace if available
    • Dress in layers
  4. Protect pipes from freezing:
    • Open cabinet doors under sinks
    • Let faucets drip slightly
    • Consider pipe insulation or heat tape
  5. Go to warming center or hotel – if temperature drops dangerously low
  6. Call HVAC professional – emergency service despite cost

What NOT to Do:

  • Never use oven for heat – carbon monoxide danger
  • Never use gas grill indoors – carbon monoxide and fire hazard
  • Never use generator indoors – carbon monoxide poisoning
  • Never use unvented kerosene heater – toxic fumes and fire risk
  • Be cautious with space heaters – leading cause of house fires

Carbon Monoxide Safety:

  • Install CO detectors on every level
  • Check batteries regularly
  • If CO alarm sounds: evacuate immediately, call 911
  • Symptoms: Headache, dizziness, nausea, confusion
  • Never ignore CO detector

Frozen Pipe Prevention:

  • When heat out, prevention critical
  • Burst pipes cause thousands in damage
  • Keep garage doors closed
  • Open cabinet doors
  • Maintain slight water drip from faucets
  • Know location of water shutoff

Preventive Maintenance

Keep Heat Running All Winter:

Monthly During Heating Season:

  • Check and replace air filter
  • Test thermostat operation
  • Listen for unusual sounds
  • Check vents for proper airflow
  • Verify outdoor unit clear of snow/debris (heat pumps)

Annual Professional Maintenance (Fall):

  • Complete system inspection
  • Clean burners and flame sensor
  • Test ignition system
  • Check gas pressure and connections
  • Clean blower assembly
  • Lubricate motors
  • Test safety controls
  • Inspect heat exchanger for cracks
  • Check venting system
  • Test thermostat calibration
  • Measure temperature rise
  • Check electrical connections
  • Test capacitors and contactors

Benefits of Annual Maintenance:

  • Prevents 95% of heating failures
  • Extends system life (20+ years vs. 15)
  • Maintains efficiency (saves 5-15% on energy)
  • Catches dangerous problems (cracked heat exchanger, CO leaks)
  • Keeps warranty valid
  • Peace of mind during cold weather

Maintenance Contract:

  • $150-300 per year typical
  • Includes annual tune-up
  • Priority service (important during cold snap)
  • Discounts on repairs
  • Many include emergency service

DIY Maintenance:

  • Change filters monthly
  • Keep outdoor unit clear
  • Test system monthly
  • Check for unusual sounds or smells
  • Respond to small issues immediately

When to Call a Professional

Call HVAC Professional If:

  • No heat and troubleshooting doesn’t resolve
  • Gas smell (evacuate and call gas company immediately)
  • Carbon monoxide detector alarming
  • Strange odors (burning, electrical, gas)
  • Loud banging, grinding, or squealing sounds
  • Water leaking from furnace
  • Repeated circuit breaker trips
  • Error codes you cannot resolve
  • Cracked heat exchanger suspected
  • System over 15 years old with major component failure
  • Any time you’re uncomfortable or unsure

Emergency vs. Regular Service:

  • Emergency rates: $200-400 just for service call
  • After-hours, weekends, holidays cost significantly more
  • If safe to wait, schedule regular service hours
  • True emergencies: gas smell, CO detection, water damage, extreme cold with no heat

Choosing HVAC Contractor:

  • Check licenses and insurance (required in most states)
  • Read online reviews (Google, Yelp, Angie’s List)
  • Get 2-3 quotes for major repairs
  • Verify up-front pricing
  • Ask about warranties (parts and labor)
  • Check Better Business Bureau rating
  • Ask neighbors for recommendations
  • Verify technicians are certified (NATE certification preferred)

Typical Repair Costs (2025):

  • Service call/diagnosis: $75-150
  • Thermostat replacement: $150-400
  • Flame sensor cleaning: $80-150
  • Ignitor replacement: $150-300
  • Blower motor capacitor: $100-250
  • Gas valve replacement: $200-400
  • Control board replacement: $300-600
  • Blower motor replacement: $400-700
  • Draft motor replacement: $400-700
  • Heat exchanger replacement: $1,200-2,500 (often better to replace system)

Repair vs. Replace Decision

Repair If:

  • System under 10 years old
  • Single component failure
  • Repair cost under $1,000
  • System well-maintained
  • No recurring problems
  • Heat exchanger intact

Replace If:

  • System over 15-20 years old
  • Multiple component failures
  • Repair cost over 50% of replacement
  • Heat exchanger cracked (safety issue)
  • Frequent repairs in recent years
  • Increasing energy bills
  • Inefficient older system (60-70% efficiency vs. 95%+ modern)
  • R-22 refrigerant system (heat pump—being phased out)

Modern System Advantages:

  • Efficiency: 95-98% AFUE (gas) vs. 60-80% old systems
  • Energy savings: 20-40% on heating bills
  • Quieter operation
  • Better comfort control (variable speed, modulating)
  • Longer warranty (10 years parts common)
  • Smart thermostat compatibility
  • Zoning capabilities
  • Improved air quality features

Payback Period:

  • Energy savings offset higher cost
  • Typically 5-10 years to break even
  • Longer in moderate climates
  • Shorter in extreme cold climates
  • Factor in repair costs avoided
  • Consider rebates and incentives

Rebates and Incentives:

  • Federal tax credits (26% in 2025 for qualifying systems)
  • State and local utility rebates
  • Manufacturer rebates
  • Financing options (0% for 12-24 months common)
  • Can reduce effective cost by $1,000-3,000+

Understanding Furnace Efficiency

AFUE Rating (Annual Fuel Utilization Efficiency):

  • Percentage of fuel converted to heat
  • Higher percentage = more efficient
  • 60-70% AFUE: Old furnaces, very inefficient
  • 80% AFUE: Standard efficiency (mid-efficiency)
  • 90-95% AFUE: High efficiency
  • 95-98.5% AFUE: Ultra-high efficiency (condensing furnaces)

Condensing vs. Non-Condensing:

  • Non-condensing: Exhaust hot (metal vent pipe), 80% efficient
  • Condensing: Exhaust cool (PVC pipe), extracts more heat, 90%+ efficient, produces condensation

BTU Output:

  • British Thermal Units measure heating capacity
  • Typical home: 40,000-120,000 BTU
  • Must be properly sized for home
  • Too small: Can’t keep up in extreme cold
  • Too large: Short-cycling, inefficient, uncomfortable

Sizing Considerations:

  • Square footage
  • Insulation quality
  • Window efficiency
  • Climate zone
  • Ceiling height
  • Home orientation
  • Professional load calculation recommended

Safety Considerations

Critical Safety Rules:

Carbon Monoxide:

  • Odorless, colorless, deadly
  • Produced by incomplete combustion
  • Symptoms: Headache, dizziness, nausea, confusion, death
  • Install CO detectors on every level
  • Test monthly
  • Replace every 5-7 years
  • Never ignore alarm—evacuate immediately

Gas Leaks:

  • Natural gas has added odor (rotten eggs)
  • If smell gas:
    1. Don’t touch electrical switches
    2. Don’t light matches or lighters
    3. Don’t use phones inside house
    4. Evacuate immediately
    5. Call gas company from outside
    6. Don’t re-enter until cleared by professionals

Electrical Safety:

  • Always turn off power before working on furnace
  • High voltage present (120V or 240V)
  • Capacitors store charge—dangerous even with power off
  • Don’t work on electrical if uncomfortable
  • Use proper tools (insulated screwdrivers)
  • Respect electrical hazards

Combustion Air:

  • Furnace needs fresh air for combustion
  • Don’t block air intakes
  • Ensure adequate ventilation
  • Especially important in tight, energy-efficient homes
  • Some furnaces require dedicated combustion air supply

Venting:

  • Must vent properly
  • Never block or restrict vents
  • Keep vents clear of snow and ice
  • Ensure proper termination outside
  • Don’t modify venting without professional
  • Improper venting causes CO poisoning

When to Stop DIY:

  • If you smell gas
  • If uncomfortable with electricity
  • If carbon monoxide suspected
  • If manufacturer warranty could be voided
  • If beyond your skill level
  • If safety concerns arise
  • If specialized tools required

Regional Considerations

Cold Climate Specifics:

  • Furnaces work harder, fail more
  • Backup heat source recommended
  • Keep emergency supplies (blankets, food, water)
  • Maintain generator if prone to power outages
  • Consider high-efficiency system for extreme cold
  • Heat pumps struggle below 25°F—may need dual-fuel system

Moderate Climate Specifics:

  • Heat pumps ideal
  • Rarely need backup heat
  • Lower annual maintenance needs
  • Longer system life (less stress)

High Altitude Considerations:

  • Gas pressure adjustments needed
  • Orifice sizes may differ
  • Professional installation critical
  • Efficiency ratings may vary

Conclusion

Heating systems that stop working are most commonly experiencing thermostat problems, power supply issues, dirty air filters, or ignition failures rather than complete system breakdowns. By verifying your thermostat is set correctly to “Heat” mode with temperature 5°F above room temperature, checking that all circuit breakers and emergency switches are on, replacing the air filter monthly during heating season, and cleaning the flame sensor on gas furnaces, you can resolve the majority of no-heat situations without professional help.

The single most critical maintenance task is replacing the air filter every month during heating season—this prevents overheating shutdowns, extends system life, maintains efficiency, and ensures adequate airflow. A dirty filter causes the high-limit switch to trip, shutting down heat production and leaving you cold. Setting a monthly calendar reminder costs nothing but prevents hours of discomfort and potentially expensive emergency service calls.

For gas furnaces, learning to clean the flame sensor—a simple five-minute task requiring only sandpaper—resolves one of the most common service calls and can be done safely by any homeowner. Similarly, knowing how to safely relight a pilot light on older furnaces provides immediate heat restoration without waiting for service.

When troubleshooting doesn’t restore heat or when you encounter gas odors, carbon monoxide concerns, or electrical issues beyond breakers, professional HVAC service is essential for safety. Annual professional maintenance in the fall prevents 95% of heating failures and catches dangerous problems like cracked heat exchangers before they become safety hazards, making the $150-250 cost one of the best investments in home safety and comfort.

With systematic troubleshooting, monthly filter changes, annual professional maintenance, and prompt response to warning signs, your heating system will provide reliable warmth throughout even the coldest winters while operating safely and efficiently for 15-20 years or more.