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LARGER VIEW of heating furnace parts and air flow, showing the heat exchanger Gas Furnaces & Heater Troubleshooting
Homeowner Checklist gives repair advice for gas-fired furnaces

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No heat or weak heat checklist for gas-fired heating furnaces.

This article gives a series of quick and easy checks and repairs for gas fired heating furnaces. The no-heat or weak heat or uneven-heat complaints experienced by most homeowners will be addressed by these easy troubleshooting steps. The text also discusses common sources of indoor condensation on windows or walls where gas fired heaters are installed and includes some important safety warnings where you see condensation indoors.

Some no-heat or inadequate-heat complaints can be easily resolved without having to call a repairman. We include safety warnings and we indicate where a service call for heat repair is almost certainly needed.



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Troubleshooting Gas Furnaces: Quick Checklist for Homeowners

Gas Furnace Troubleshooting Checklist

Watch Out: Immediate LP or natural gas safety hazards: if there is evidence of an LP or natural gas leak at a building, gas odors, for example, you should:

Do not do anything that is likely to cause a gas explosion, such as lighting a match, operating an electrical switch, or even using a telephone in the building
Leave the building immediately
Notify other building occupants of the safety concern
Contact the local gas company and/or fire department

No Heat or Not Enough Heat from the furnace

Possible Cause Action Comments & More Help
Furnace won't turn on Check that power is on to the unit

Some WALL-MOUNTED FURNACES can operate without external electrical power.

FURNACE CONTROLS & SWITCHES

HEAT WON'T TURN ON

Thermostat not properly set Set thermostat to above current room temperature. Check that thermostat is set to HEAT mode. THERMOSTATS, HEATING / COOLING
Pilot light is out Check pilot, re-light.
Check that fuel supply is turned on.

If pilot won't stay lit check fuel supply.
Check for or replace thermocouple.

THERMOCOUPLES

Pilot on, burner won't turn on Check that gas valve is set to ON, not PILOT GAS REGULATORS for APPLIANCES
Burner not operating properly: noisy, incomplete, uneven, weak flame, flame lifts off burner. Service call required. GAS BURNER FLAME & NOISE DEFECTS
 

Insufficient warm air circulation from the gas furnace

Possible Cause Action Comments & More Help
Dirty air filter Clean or replace the air filter

AIR FILTERS for HVAC SYSTEMS

Air supply registers obstructed Clean dirty register outlet grilles; remove blocking furniture, carpet, etc. AIR FLOW IMPROVEMENT, HVAC
Return air registers obstructed Clean dirty register return air inlet grilles; remove blocking furniture, carpet, etc. INCREASING RETURN AIR
Dirty blower fan Clean dirty blower fan assembly. Small amount of dirt greatly decreases air movement DIRTY A/C BLOWERS
 

Floors are too cold

Possible Cause Action Comments & More Help
Blocked return air inlets   INCREASING RETURN AIR
Dirty air filter Clean or replace the air filter

AIR FILTERS for HVAC SYSTEMS

Inadequate air circulation: warm at ceiling cool at floor Set blower for continuous operation BLOWER FAN CONTINUOUS OPERATION
 

Noisy Furnace: blower or burner noises

Possible Cause Action Comments & More Help
Noisy blower fan

Blower may need oiling

Blower fan bearings loose, worn

Blower is dirty or air filter is dirty, clogged

AIR FILTERS for HVAC SYSTEMS

BLOWER FAN OPERATION & TESTING

Noisy gas burner Service call required , gas regulator defect, combustion air defect

Watch out: system may be unsafe. Shut it down.

GAS BURNER FLAME & NOISE DEFECTS

 

Moisture condensing on windows or walls - gas fired heat

Possible Cause Action Comments & More Help
Blocked chimney or exhaust vent

Inspect & clear, repair, replace improper venting.

Service call required.

Watch out: the heating system is likely to be unsafe. Shut it down.
Combustion air inadequate Service call required.

Watch out: the heating system is unsafe. Shut it down.

CARBON MONOXIDE - CO

COMBUSTION AIR REQUIREMENTS

Insufficient ventilation, tight house. Service call required.

Watch out: the heating system may be unsafe. Shut it down.

COMBUSTION AIR for TIGHT BUILDINGS

Humidifier improperly set Check power humidifier or free-standing humidifier settings. Also see DUCT & AIR HANDLER ODORS

Notes:

Watch out: improper installation and even improper inspection and testing methods involving natural or "LP" gas can involve dangerous conditions and risk fire or explosion.

See DIAGNOSE & FIX HEATING PROBLEMS-FURNACE for complete diagnostic & inspection guides

Adapted from Sears Corporation, "Sears Gas Furnace Service Hints", (1993), provided courtesy Jim Jagger, ASHI, Buckeye Home Inspections, Cleveland OH, Tel: 216-486-4663. Sears Gas-Fired "Space Saver"Furnace Models: 867.765030 - 867.775260.

 

Direct Vent Gas Furnace Product Sources & Inspection / Installation Information

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