Gas Furnace Repair & Troubleshooting: Fixes You Can Do

If your heat is not working, this gas furnace repair and troubleshooting guide will help you. We’ve included fixes for common problems that we find during winter furnace complaints. Hopefully you’ll be able to get your furnace back to heating your home. If not, this troubleshooting before your technician arrives will help narrow down the potential problem.

Check Your Furnace Filter

Furnace filters require regular maintenance because they fill up with dust. A dirty filter can reduce the efficiency of your furnace and not produce enough heat. In some cases, it even stops the furnace from turning on.

Depending on your home, the number of pets you have, and your filter type, you may need to replace your filter every month, every six months, or every year. For example, if you have a HEPA filter then you might need to replace the filter every year since it takes a long time to fill up with dust.

Check Your Thermostat

First check your thermostat batteries and replace them if need be. This is a common problem that HVAC technicians see too often.

The furnace may not be turning on because the temperature on your thermostat is set too low. Try setting it about 5 degrees higher than the room temperature. If your furnace turns on, then you know your furnace and thermostat are working.

Thermostat Location

If you find yourself having to increase the temperature and wait for the furnace to turn on, there may be a problem with the location of your thermostat. We suggest installing your thermostat away from sunlight, doors or windows, sources of air or draft, and away from heat sources. All these will interfere with the thermostat reading and will trigger your heating unit to turn on/off inappropriately.

Programmable Thermostats

If you have a programmable thermostat, make sure any preprogrammed setting is not stopping your furnace from turning on. For example, you may have set the temperature to be 72 degrees at night. If the house is already at 72 degrees but you want to make it warmer, then you need to change the programmed settings first.

Look at your Circuit Breaker

If your tried setting the temperature a few degrees above the room temperature and the furnace didn’t turn on, try checking the circuit breaker. If you had any electrical work done recently, the furnace circuit breaker may have been tripped or blown. If the breaker has been tripped, it’ll be in the center position, which you’ll want to change to on.

Check the Furnace Switch

It’s a good idea to see if you have power to your furnace. Check the furnace power switch and make sure it’s in the on position. If you have a fuse next to the furnace switch, see if the fuse is broken. If it is broken, you need to replace it with a new one. Make sure it has the same ampere rating as the old fuse.

Also check if your furnace is connected to gas. Usually the gas connection in a furnace looks like this:

Check the Standing Pilot Furnace Flame

The flame from your standing pilot light should be blue—this means that the gas is being burned properly. If the flame is a different color, there is a problem. You will need to call a professional to see why the flame color is not blue. It may be because the burners are dusty or dirty. We suggest cleaning the burners every year.

If there is no flame in your furnace, you can relight it. The flame may go out for many reasons, such as a buildup of condensation, too much or too little air supply, inconsistent gas pressure, or hardware issues. If you decide to relight the pilot yourself, make sure to follow the instructions in your furnace’s manual closely and take safety precautions. Make sure to have good ventilation and turn off the gas 20 minutes before you try relighting the pilot.

Check Your Limit Switch

The furnace limit switch commands your furnace’s circuit board. It also acts as a safety device that prevents overheating. The limit switch may malfunction and lead to issues, such as the furnace overheating. A professional can easily replace the limit switch.

Clean Flame Sensor

The flame sensor may malfunction if it has a buildup of dirt, which results in the furnace failing to start. You can clean your flame sensor by yourself, and you can try following these steps:

  1. Turn the furnace off completely beforehand.
  2. Access the combustion chamber of your furnace.
  3. Then, remove the flame sensor and remove dust with steel wool. Lightly clean the remaining dust with a soft cloth or tissue. 
  4. Lastly, remove dust from the electronic igniter and pilot and then replace the furnace flame sensor. After closing the combustion chamber door, you can restart the furnace.
Flame Sensor

Check the Front Panel of the Furnace

A built-in safety mechanism of some furnaces is that the front panel must be secured. If it’s loose, the furnace will not work because the fan and burner will not operate.

Ensure all Vents are Open and Cleared

Vents around your home may be surrounded by furniture or curtains. Clear the area around vents and ensure they’re all open.

Call Your HVAC Technician

If none of these furnace repairs or tips worked, then it’s time to call your HVAC technician. Hopefully you’ve narrowed down what’s not the problem and can help your technician get through the troubleshooting faster. Try explaining the specific issue at hand in detail, describe what you’ve tried fixing or cleaning, and the technician may be able to diagnose the problem over the phone. Whatever it is, getting your furnace fixed quickly is important in the cold winter months, so don’t hesitate too long to call for help.  

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