Heating & Cooling Combined Unit: Why won’t my furnace burners won’t stay lit?

When your furnace burners ignite then shut off after several seconds, the flame sensor is likely dirty or it needs replacing. The flame sensor detects burner flames and shuts off gas going to the burners if it doesn’t detect burner flames.

You can shut off power to the furnace and clean the flame sensor using steel wool. Wipe the sensor with a cloth and reinstall it. Test the furnace to see if the flames keep burning. If not, then you’ll likely need to replace the flame sensor.

Less frequent causes of the furnace flame only igniting for a few seconds are damaged burners, lack of air flow and a bad high-temperature limit switch.

If you’re not able to determine why your furnace flames won’t stay lit, have a service technician diagnose and repair the furnace.

heating & cooling combined unit

THESE REPAIRS MAY HELP SOLVE YOUR HEATING & COOLING COMBINED UNIT PROBLEM

Clean the furnace flame sensor

Clean the furnace burner flame sensor

When the furnace burner ignites and only stays on for a few seconds, the flame sensor may be dirty. You can shut off power to the furnace and clean the flame sensor to troubleshoot the problem. You’ll typically find the flame sensor on the front burner box panel but the sensor can be located on the top or bottom of the burner housing as well. Remove the burner access panel and disconnect the flame sensor wire. Remove the flame sensor and clean it with steel wool. Wipe residue off the flame sensor and reinstall it. Reassemble the furnace and test burner operation. If burners stay lit, then cleaning the flame sensor fixed the burner problem. If flames still go out after a few seconds, then you may need to replace the flame sensor.

Clean the furnace burner flame sensor

Find the required part specific to your product.

Replace the furnace flame sensor

Replace the furnace flame sensor

When the furnace burners only stay lit for a few seconds, a faulty flame sensor may be causing the failure. You can try cleaning the flame sensor to fix the problem. If flames don’t stay lit after cleaning the flame sensor, you’ll likely need to replace it.

Shut off electrical power for the furnace and remove the burner access cover. Disconnect the flame sensor wire and remove the flame sensor mounting screw. Pull the flame sensor out and replace it. Reassemble the furnace and restore electrical power.

Furnace flame sensor

Find the required part specific to your product.

Replace the furnace flame sensor
March 16, 2022By Sears PartsDirect staff

How to replace the furnace flame sensor

Learn how to replace the flame sensor in your gas furnace when it doesn't detect the flame and the burners only light for a few seconds.

Repair difficulty
Time required
 15 minutes or less

Symptoms common to all heating & cooling combined units

Choose a symptom to see related heating and air conditioning system repairs.

Dirty air filter, clogged condenser coils, low refrigerant charge, faulty compressor
Thermostat problem, clogged air filter, burner failure
Dirty flame sensor, failed flame sensor, damaged burner, bad high limit switch
Thermostat problems, bad compressor/condenser fan capacitor, lack of refrigerant, failed compressor
Main causes: errant thermostat settings, lack of electrical power, clogged drain line, wiring failure, control failure.
Main causes: Errant thermostat settings, lack of power, bad interlock switches, lack of exhaust ventilation, wiring failures.

Repair guides common to all heating & cooling combined units

These step-by-step repair guides will help you safely fix what’s broken on your HVAC system.

March 16, 2022
By Sears PartsDirect staff
How to unclog the air conditioner drain line

The condensate drain line for your central air conditioner can clog with mold and mildew. Water will back up and start dripping below the inside air conditioner unit. Follow the steps in this guide to unclog the drain pipe.

Repair difficulty
Time required
 15 minutes or less
March 16, 2022
By Sears PartsDirect staff
How to replace the furnace flame sensor

The flame sensor detects when furnace burner flames are lit. You may need to replace the flame sensor if flames only stay on for a few seconds.

Repair difficulty
Time required
 15 minutes or less
How to replace a heating and air conditioning system thermostat

The control thermostat for your HVAC system can stop working. This repair guide shows how to replace it.

Repair difficulty
Time required
 30 minutes or less

Articles and videos common to all heating & cooling combined units

Use the advice and tips in these articles and videos to get the most out of your HVAC system.

February 22, 2022

Why is my furnace not igniting?

By Lyle Weischwill

Find out why the burner on your furnace isn't igniting.

February 22, 2022

Can a furnace be repaired?

By Lyle Weischwill

Learn about furnace repairs and how much they cost.

February 23, 2016

What to check if your air conditioner isn't cooling video

By Sears PartsDirect staff

If your central air conditioner isn't cooling as it should, we'll show you how to check for a tripped float switch and clogs in the drain pipe.