Gas Furnaces & Heater Troubleshooting
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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
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
Gas Furnace Troubleshooting Checklist |
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No Heat or Not Enough Heat from the furnace |
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| 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. |
| 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. |
| 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 |
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| Possible Cause | Action | Comments & More Help |
| Dirty air filter | Clean or replace the air filter | |
| 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. | RETURN AIR, INCREASE |
| Dirty blower fan | Clean dirty blower fan assembly. Small amount of dirt greatly decreases air movement | DIRTY A/C BLOWERS |
Floors are too cold |
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| Possible Cause | Action | Comments & More Help |
| Blocked return air inlets | RETURN AIR, INCREASE | |
| Dirty air filter | Clean or replace the air filter | |
| Inadequate air circulation: warm at ceiling cool at floor | Set blower for continuous operation | BLOWER FAN CONTINUOUS OPERATION |
Noisy Furnace: blower or burner noises |
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| 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 |
|
| Noisy gas burner | Service call required , gas regulator defect, combustion air defect | Watch out: : system may be unsafe. Shut it down. |
Moisture condensing on windows or walls - gas fired heat |
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| 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. |
| Insufficient ventilation, tight house. | Service call required. | Watch out: : the heating system may be unsafe. Shut it down. |
| Humidifier improperly set | Check power humidifier or free-standing humidifier settings. | Also see DUCT & AIR HANDLER ODORS |
Notes to the table above
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
- Casey, Michael & Hansen, Douglas, Robinson, Roger, "Wall Furnaces", CREIA Inspector (1999).
- 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.
- Trane Corporation, "Upflow/Horizontal Left Downflow/Horizontal Right Condensing Direct Vent Gas-Fired Furnace" XR90 TUX040 - TUX120C Single-Stage Fan Assisted Combustion System, TUXC-D2, American Standard, Inc., (2003), Website: www.trane.com, Louisville Kentucky. Furnaces certified by AGA and CSA.
- Williams Furnace Company, "Direct-Vent Furnaces", (2012) Williams Furnace Corporation, 250 West Laurel St., Colton CA 92324, USA, Tel: 909-825-0993, Consumers: 888-256-6465, Homeowners: 909-426-0978, Website: www.e-wfc.com
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Reader Comments, Questions & Answers About The Article Above
Below you will find questions and answers previously posted on this page at its page bottom reader comment box.
Reader Q&A - also see RECOMMENDED ARTICLES & FAQs
Why is the pilot light on my gas furnace flickering?
Pilot light flickering - On 2018-12-09 by kathy
by (mod) - Pilot light flickering
Dirty orifice
Loose connection
Improper placement
Low fuel?
Why does my furnace blower never shut off?
What caused the furnace blower to run not shut off - On 2018-12-01 by Jerry
Answer by - by (mod) -
Jerry
The explanation and diagnostic steps for a furnace or air handler blower fan that never stops are
Thank you to our readers for their generous comments
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. - On 2021-02-11 by Green Leaf Air
Moderator note: Thank you Green Leaf: while our policy does not permit readers to post self-promotions, ads, links, we welcome content criticism, suggestions, comments and are happy to identify and link to such technical contributors.
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Continue reading at DIAGNOSE & FIX FURNACE PROBLEMS or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.
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- NO HEAT - FURNACE
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