Gas Furnace Troubleshooting or Any Furnace Repair should only be done by a qualified HVAC Technician
Gas Furnace Troubleshooting & Repair - Aside from understanding the basics of electrical, Electronics and controls to troubleshoot a furnace one needs to understand the components of the furnace and the gas furnace sequence of operation. Therefore repair techniques for various furnaces will be different from furnace to furnace depending on what type of furnace you are repairing. This is a basic gas furnace repair article that simply covers the basics. If you want to learn more about repairing furnaces you can check out the recommended reading and get a book on HVAC or Furnaces or another option is to take a repair class at your local community college or trade school. Of course, you can’t learn it all in a book nor taking a repair class but you can learn the basics of repairing furnaces by learning the basics of HVAC. After all, nothing beats experience, especially educated experience.
Always remember that when repairing any appliance and you are ever in any doubt it is best to call professional. If you ever smell gas open your windows and leave. Do not turn any light switches on or off or light any matches or any type of fire. Go outside an call your local HVAC contractor or the utility company. Let them check everything out. Don’t take any chances.
Gas Furnace Troubleshooting & Repair – The Thermostat
The first thing I always do when arriving on a repair call for no heat is to talk to the homeowner and see if they have any input such as describing any strange noises or anything else they want to offer about unusual observation of the furnace. The next thing I do is to find the thermostat and make sure it is set for heating and the temperature is turned all the way up as far as it will go. If it is a mechanical thermostat you can check to make sure the heating anticipator is intact by making a visual inspection of the thermostat as many mechanical type thermostats you visually see the circuit for the heating anticipator. It is also a good time to ask the homeowner about the service. Have they paid the gas bill. You can check the meter to make it is not locked out. There are instances where the homeowner paid the bill but the utility company red tagged the meter because they sensed a leak in the line near or at the home. Occasionally utility companies will send out people with special combustible gas detectors to check for leaks in their lines and homes that are served by their lines.
Gas Furnace Troubleshooting & Repair – Checking the Air Filter
The next thing to do is to check the air filter which should near the thermostat somewhere. If the air filter is loaded up it has not been changed for a long time. This can be the problem as the loaded up air filter will impede the airflow and set off the high limit switch in the heat exchanger. This high limit should automatically reset itself but I have seen them not reset themselves and the high limit switch needs to be replaced with an exact replacement. Never jump it out and leave the job. That is very dangerous and highly discouraged.
Gas Furnace Troubleshooting & Repair - Supply Vents Open?
While you are at the filter and have the homeowner there you can ask about the supply vents. Make sure they ARE ALL OPEN. I have found some situations where the homeowner closed off to many vents and it has the same effect as having a dirty furnace air filter. I always get a “I don’t know from the homeowner which means I go around and visually check all the supply vents I can find. I have never failed to find at least one or two supply vents that were closed and in a few cases, I found multiple supply vents closed and that was the problem causing the furnace to malfunction. Open those supply vents to make sure that the furnace has the appropriate airflow.
Gas Furnace Troubleshooting & Repair - Blower Motor Check
We finally make it to the furnace itself and we begin making basic checks having eliminated all the aforementioned problems. We check to make sure the blower motor is functioning properly. To do this we must determine how the blower motor is controlled. Is it controlled by a fan limit control? A Printed Circuit Board? or a relay that is hooked to another device? If the blower motor is working is can easily be checked by jumping the relay if it is controlled by a relay. If it is controlled by a fan limit control we can manually adjust the fan limit control until the blower comes on. If a printed circuit board we can use a multi-meter to check the voltage from the fan terminal to make sure it is getting proper voltage to the fan motor. If it is getting the proper voltage but the blower fan is not working then we need to look at the blower fan motor. Check the motor run capacitor and other things with the fan. If we are not getting voltage to the fan motor we need to find out why.
Gas Furnace Troubleshooting & Repair - Other Furnace Component Checks
There are other components of the furnace we need to check including the furnace igniter, the gas furnace ignition controls, and making sure the valve is opening as it should. Inside the furnace itself there are multiple safeties that need to be check and the safety circuit for the furnace is typically uses 24 volts so this will require us to check the transformer inside the furnace. Other things in the process of troubleshooting a furnace include, the ignition process, the safety circuit, the forced draft or induced draft motor, the flame sensor, and a check of the exhaust system or flue to make sure the furnace properly exhausts the gasses. As stated above, there are many different types of furnaces and each furnace will require different methods of troubleshooting. A trained HVAC technician can properly, safely, and efficiently troubleshoot your furnace. Always make sure as a homeowner that you get regular annual furnace preventive maintenance on your furnace and that will likely prevent anyone from having to troubleshoot your furnace because it is properly maintained.