Furnace Troubleshooting Guide

HVAC Logo IconBy Tom MoorAugust 1, 2023


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Technician repairing Gas Furnace

When the first snow falls, it is easy to feel cozy inside your home — if your furnace is working well, that is. Like most hardworking appliances, furnaces require regular upkeep and routine maintenance. According to the NY Times Annual Home Maintenance Checklist, an HVAC professional should check your house’s ductwork and clean your furnace on a bi-annual basis to keep everything running smoothly.

If you have already scheduled routine maintenance yet your furnace seems to be malfunctioning — e.g., blowing cold air or perhaps blowing no air at all — you might try these furnace troubleshooting tips.

Troubleshooting Tips

Sometimes troubleshooting your furnace is a simply a matter of reviewing the obvious, like making sure the thermostat is set properly and batteries are working. When issues become more complicated, call an HVAC professional. In the meantime, try this quick review yourself:

1. Make Sure the Thermostat Is Set Properly

Confirm that your thermostat is set on “heat” and the temperature is positioned where you want it. Perhaps someone in your home turned down the thermostat or accidentally flipped the switch. If the thermostat is set properly, turn it up a few degrees to see if that makes a difference.

2. Change Thermostat Batteries

If you have a battery-powered thermostat, make sure its batteries are working. If they are dead, the thermostat cannot communicate with the furnace. Change batteries to see if that solves your problem.

3. Replace Furnace Filter

Dirty filters affect the air quality in your home and can shut off your furnace (especially newer gas furnaces, which turn off to avoid overheating). Furnace filters should be changed every 30-90 days to allow for proper air flow.

4. Check Circuit Breakers

Could you have blown a fuse? Locate your fuse box, and look for the switch marked “furnace.” If no such marker exists, then look for the switch flipped opposite of all the others, and then flip it back.

5. Check Fuel Source

Take care with this troubleshooting tip since gas or propane is involved. See if your valve was somehow turned off by accident. If you smell gas, contact an HVAC professional immediately to handle any natural gas leaks, as they can be dangerous.

When to Contact an HVAC Professional

If the furnace troubleshooting checklist did not alleviate your issue or you ran into one of the problems below, then call your local HVAC professional to get your furnace working again.

  • Noisy Furnace: If your furnace is clanging, banging, or making other noises, this could be a symptom of a serious problem. Call a professional.
  • Gas Line Issue: Leave a natural gas problem to the professionals since it can be dangerous.
  • Faulty Pilot Light or Furnace Flame: If your pilot light keeps going out, contact a professional, as the ignition switch may be installed incorrectly.
  • Improperly Installed Furnace: If your furnace was installed wrong, then it could be leaking gas or carbon monoxide into your home. Again, call a professional.

Experienced professionals can troubleshoot these furnace problems and get your home warm again.

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Furnace FAQs

How do I reset my furnace?

Most furnaces have a reset button on the top, on the side, or on the bottom. Check your owner’s manual for the exact location. If you have a Lennox furnace, here’s a troubleshooting guide, for example. Each manufacturer will have its own.

Why is my furnace not coming on?

If your furnace is not on and you have tried the furnace troubleshooting tips above, then contact your local HVAC professional.

How do you know if your furnace went out?

Referring to the furnace’s manual for its location, see if your pilot light is on. The main gas line coming into your home may be off for some reason; a call to your gas company should alleviate this.  If you are having furnace problems, plenty of furnace troubleshooting tips exist. That said, if they do not work for you or if you feel uncomfortable completing any of them, give your local HVAC professionals a call. They can assess any issues and then repair your furnace so your home can be cozy again. 



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