Gas Furnace Troubleshooting

By reading this furnace troubleshooting guide, you may be able to repair your gas furnace yourself and save some money. The average call-out charge for a furnace repair service will cost you over $100, so troubleshooting your gas furnace could well be worth considering before making that phone call. If you are wondering exactly what this is, this step-by-step guide will show you, and further explain how you can diagnose and repair common gas furnace problems yourself. At this point, it is important to note that only you alone know how capable you are of performing this activity properly and safely. This is simply a guide, and therefore should be read with discretion for your particular situation.

Correct furnace maintenance is often the best way you can prevent most common furnace faults from occurring. For furnace troubleshooting results to be effective, you must ensure that you have carried out and followed the basic maintenance tasks as instructed in your furnace manual. This troubleshooting guide can be used for furnaces that use natural gas or propane.

The first place to start your diagnosis is at the thermostat, making sure that it is set to heat above room temperature. The furnace fan should also be running. If it is currently not, then you should place it in the on mode.

Then continue troubleshooting by heading over to the furnace. If the fan is still not running after setting it in the on mode, check that the circuit breaker was not tripped. Keep the breaker switched off and ensure that there are no loose connections among the furnace wiring. While you’re at it, you should also look for burn marks on the control board, and replace the board if any such marks can be seen. After performing any required repairs, you can reset the breaker. In the event that the neither the breaker or fuse were tripped, it means the fault could lie with the blower motor, furnace control board, the transformer, the run capacitor, or even the thermostat itself.

Common furnace problems:

  • For furnaces that use a standing pilot, the flame should always be touching the tip of the thermocouple. If it doesn’t, you will need to carry out a more in-depth furnace troubleshooting to find out if the thermocouple needs to be replaced.
  • Often the main burners may not come on even though the furnace pilot is lit. To properly troubleshoot in this situation, you should first feel the side of your furnace. If it is cool, this indicates that the problem could be coming from the limit control, thermostat, gas valve or furnace control board. On the other hand, if the side of the furnace is warm, you should allow the unit to cool before continuing to troubleshoot your furnace.
  • If your furnace has an inducer motor, and after you have checked it you find out it is not running, then the problem could be with the furnace control board or the inducer motor itself. Check to see if the pilot tries to ignite when the inducer motor is running. If it doesn’t, it’s likely that the flue is blocked, the furnace control board is damaged, or that there is a fault with the limit control.

These are just some of the problems you may have encountered while using your furnace. It’s good practice to complete your furnace troubleshooting steps by observing how the furnace operates while going through a complete heating cycle. When the cycle has completed, the fan should continue to run for 2-3 minutes once the burner shuts off. If the fan does not shut off after this time delay, then the fan and/or limit control (especially on older units) may be sticking and therefore requiring a replacement.