DIY Furnace Troubleshooting

Furnace problems can be inconvenient, especially if they occur during a prolonged cold spell. Being able to troubleshoot heating problems for a furnace can save you the cost of a service call. As you do your own furnace troubleshooting, it’s important to know your own limitations. If you have any doubts about troubleshooting a particular part of the furnace, such as the gas ignition system, don’t hesitate to call a service technician.

Instructions

1. Start with the thermostat. The thermostat should be set to heat and not air conditioning. Make sure that the set point for the furnace to operate is higher than the room temperature and that the fan is the “On” position.

2. Check the breaker box to make sure the breakers to the furnace are on. A tripped breaker indicates that there may be loose wiring or a bad control board in the furnace. Check all the wiring for worn spots. Examine the control board for burned-looking areas. Repair any bad wiring, and/or replace the control board. Switch the breaker back on.

3. Look inside the reservoir of the condensate pump. If it’s full, the pump isn’t working properly. Replace it.

4. Touch the side of the furnace. A cool furnace indicates there might be a problem with the thermostat, furnace control board, limit control or gas valve on a gas furnace. A warm furnace indicates the problem may be in the inducer motor or the furnace control board. Depending on your electrical expertise, you may want to call a technician to make these repairs.

5. Read the meter on the propane tank, if that’s what your furnace uses for fuel, to make sure you aren’t out of gas. If you have a supply of gas, it’s possible that there may not be enough gas reaching the furnace. It’s best to let a service technician adjust gas flow to the furnace.

6. Watch the ignition cycle of the furnace. If your gas furnace has a continuous pilot light, you should see a flame. If the furnace uses an igniter, check that it’s making sparks to ignite the gas. If you see no signs of ignition, replace the ignitor. Be careful not to touch the glass tubes of the ignitor as you install it or you can ruin it. On an electric furnace, you should see the heating element warm up.

7. Time how long it takes for the ignitor to light the burners of your gas furnace. If it takes longer than three seconds, the flame sensor may be defective. Replace it. If the burners don’t stay lit, try cleaning the condensate drain. This can help provide more air for to help keep the fire lit.

8. Listen for the blower motor to run. It should start one to three minutes after the burners ignite on a gas furnace. If the blower motor isn’t running, make sure the motor has electricity running to it. If that’s not the problem, you need to call a service technician. In the meantime, turn off power and gas to the furnace.

Tips & Warnings

• Follow the specific directions in the service manual for your furnace as you change any parts on it.

• Always turn the power off to the furnace as you make repairs.

References

• HVAC for Beginners: Furnace Troubleshooting, Before You Call the Repairman
• Arnold Service: Troubleshooting Heating Problems