Before calling a service company out, here are some basic furnace troubleshooting tips that you can easily run through yourself and save $$$.
1. Check Thermostat Batteries
Remove and replace batteries. The thermostat signals the furnace to come on based on the internal temperature sensor. Failing or dead batteries can cause loss of communication with the furnace and cause it not to come on.
2. Check Furnace Power Switch
Flip switch to on position. Make sure the breaker is not tripped. This happens more often thank you think!
3. Check For a Tripped Breaker
Turn breaker all the way off then flip back to on position. Sometimes this can be an indication of failing components such as a motor overamping. If the breaker trips again, make sure to give us a call.
4. Check for Closed Vent Registers and Obstructed Return Grilles
Open blocked off registers. Make sure return vents aren’t blocked by furniture. Airflow is everything for proper operation of your furnace. Blocked off registers and return grilles can cause lack of airflow and cause your furnace to overheat and trip the high limit safety switch. Additionally, this can cause your blower motor to work harder and overheat and cause premature motor failure. If you barely feel any air from the registers, check the rest of the registers and return grilles and filter to ensure you have proper air flow. If you still lack proper air flow, check the blower wheel for dirt build-up and missing fins.
5. Inspect Furnace Filter
Replace dirty filter. A filter should be replaced every 30 days, or 90 for 3”+ filters. A dirty filter and restrict air flow and cause the furnace to overheat and can cause overall air quality issues.
6. Inspect Flame Sensor
A dirty flame sensor can cause the furnace to fire and shut off immediately or intermittently. We recommend replacing flame sensors as they are a low-cost part and cleaning them can damage them over time. If you elect to clean your flame sensor, make sure to use virgin-steel wool.
7. Inspect Wiring and Connections
Bad wiring can cause myriad issues. Ensure that connections are properly seated and wire nuts are secured. Also look for burn marks on the wiring. We have seen it all and improper service is usually the culprit.
8. Secure Loose Furnace Panels
A furnace will not operate with an open blower compartment. Ensure that the furnace panels are secured. Furnaces are equipped with a door safety switch that acts as a safety feature to protect injury from a spinning blower wheel. Along with that, it ensures proper airflow through the blower compartment to prevent combustible gases from entering the home.
9. Inspect Furnace Exhaust Flue
We have seen this one quite a bit in the service industry- clogged flue pipes frozen over or obstructed with debris from critters or children stuffing the exhaust pipe with rocks and dirt. This causes the pressure switch no not close or open as needed. Inspect the exhaust pipe for obstructions and remove as necessary. Also those in winter climates may find the exhaust flue frozen over either due to improper placement or vent grilles. While it may be tempting to put a grille over the exhaust flue to keep critters out, this can cause moisture to collect and freeze, causing your furnace to not operate. Also check for nearby furniture as closely-placed items can cause the pipe to freeze over, or even worse, combustion gases entering the home.
10. Check for Proper Combustion Air
For high-efficiency furnaces, make sure the intake pipe is clear of debris. For older 70-80% furnaces make sure that the furnace is receiving enough ambient combustion air. Sometimes the "tightening" of a house by sealing windows, doors, etc can cause an unforeseen impact by not letting in enough outside air. This would be remedied by a make-up air installation. If you happened to remodel your house and wanted to hide your ugly furnace by stuffing it in a closet, beware that you may have possible lost proper combustion air for your furnace to operate properly. Make sure the area around the furnace is free of debris and obstructions.
If you have any furnace questions, or need help finding furnace replacement parts, contact us!
About the Author
James Clark is the HVAC Controls Specialist and Ecommerce Manager for Technical Hot & Cold. He has been with the company since 2014 and enjoys helping homeowners save money by providing help articles that walk them through various DIY HVAC repairs. In his spare time, he's playing music with his children and spending too much time working on his lawn.