Skip to main content

Furnace issues? Try these furnace troubleshooting tips


The cold truth of the matter is, sometimes your furnace misbehaves at the worst possible time – when you are counting on it for warm, winter comfort. 

But here’s some information you can warm up to: there are a number of issues most average homeowners can solve on their own. So, before you contact the first available HVAC contractor, take a few moments to follow these troubleshooting tips. You might find the solution yourself... and save the time and expense of an unnecessary service call.

Furnace not running 

Check the thermostat: Make sure it wasn't inadvertently turned off, and that it is set on “heat” or “auto.” Also check the temperature setting – if the temperature inside is warmer than the thermostat’s setting, the furnace won’t kick on. And if you have a battery-powered thermostat, try changing the batteries.

Check for a power interruption:  Your furnace needs electricity for its control board and motors. Locate the power switch on the side of the furnace – it looks like a light switch – and be sure it’s on. Then, check your breaker box to be sure the furnace breaker is in the “on” position. 

Check your air filter: An extremely dirty or clogged furnace filter can block airflow causing the furnace to overheat and shut down. Replace the filter if necessary.

Furnace Starts, Then Stops 

A furnace that starts up but then stops quickly usually means one of three things:

  • An excessively dirty furnace filter.
  • A bad flame sensor.
  • Failing thermostat.

Start by checking the filter. If it's clean, it’s probably time to call a professional. The other usual suspects that often cause this issue are best diagnosed by a professional as well.

Cool or Weak Airflow 

  • Check the thermostat: Some systems can run the blower fan continuously for ventilation, even when the furnace isn’t heating. If you don’t want this operation, check that your thermostat is set for heating, and switch it to “auto” mode instead of “on” so the fan will only run when the furnace is warming the air. 
  • Check the furnace filter: An excessively dirty filter can reduce airflow. Replace it if necessary.
  • Check your fuel source: If it’s a natural gas furnace, check the gas shutoff valve leading into the furnace to be sure it is in the “on” position. If you have an oil or propane furnace, check to be sure your tanks aren’t empty. And, if you have an older furnace, check that the pilot light is lit.

Still not feeling the heat? Give our furnace troubleshooting page a read.  Then, call a Carrier HVAC contractor, who has the tools and training to get your system up and running – and your family comfortable again.