Troubleshooting Tips for a Malfunctioning Gas Furnace

Although you probably don’t use your furnace as often as your A/C, knowing how to troubleshoot a gas furnace will help you get it running quickly and efficiently, especially during cold, winter nights and the occasional cold front. Starting it up again after it stops will keep you and your family more comfortable. Who knows, you might even be able to avoid a service call.

When It Won’t Run

Check the thermostat to be sure it’s set to “heat” and increase the temperature a few degrees. If it doesn’t start after a few minutes, go to the circuit breaker and reset it. Then, check the gas supply to the furnace and make sure the valve is on.

If your furnace has a pilot light, check that it’s burning. If it’s out, light it again. If you’re unsuccessful, the light and the thermocouple may need cleaning.

It Runs, But Doesn’t Produce Enough Heat

If your furnace starts for only a short time, check the air filter. Gas furnaces have safety switches that turn them off when too much heat builds inside it. If the filter was the culprit, the system should run normally now.

If the filter is clean, open the door to the burner and look at the flame quality. If there’s any yellow or uneven distribution of flame, call your HVAC contractor for maintenance and cleaning.

Runs for Short Periods

When troubleshooting a gas furnace, verify that your system doesn’t use a pilot. If it doesn’t, it might have a hot surface ignition system that can wear out over time. If the furnace won’t run more than a few seconds, this part may have failed and needs a replacement by an HVAC professional. Given our mild temperatures, your home may not need as much heating, causing the furnace to stop shortly after starting up.

Runs, But Air Feels Cold

When the heating cycle stops, indoor air gradually cools down, but the fan still circulates it if the thermostat is set to “fan,” so change the fan setting to “auto.”

The pros at CCAC can help you troubleshoot a gas furnace. We’ve been providing exceptional HVAC services for Texas homeowners since 1979.

Our goal is to help educate our customers in Corpus Christi, Texas about energy and home comfort issues (specific to HVAC systems). For more information about furnace troubleshooting and other HVAC topics, download our free Home Comfort Resource guide.

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