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My Furnace Is Not Turning On!

DIY List on How to Troubleshoot Common Furnace Problems That Cause Your Furnace Not to Start

Winter weather is starting to set in here in Cincinnati, OH. If you know Ohio weather then you know that could mean a random 60-degree spring day at times, but most likely it will mean a lot of bitterly cold days and not a lot of sunshine. During these times it is crucial that your furnace starts up and heats properly so you can stay comfortable.

If your furnace won’t turn on there are a few simple DIY things you can check before calling for a furnace repair pro. We’ll go through how to check some reasons why your furnace won’t start up.

1. Check the circuit breaker

Go to your breaker box and check to see if a breaker has flipped (hopefully your box is nicely labeled so the furnace breaker is easy to find!) This is still important to check even if you have a propane or gas furnace. If you find the breaker is in the “off” position, try turning it back on to see if that fixes the issue. If the breaker repeatedly trips, then it is time to call for HVAC repair. If other appliances are also not working, the chances of it being an electrical problem are probably high.

2. Check the thermostat

It sounds simple, but make sure that your thermostat is in heat mode and turned on. We’ve gotten a lot of calls from thermostats simply still being set to AC mode.

If the thermostat display is not lit, then you may need to change the batteries.

Finally, check to make sure you don’t have a schedule set that may be keeping it cooler in the house than you would like. When using a programmable thermostat with scheduling features you may have it set to be cooler during times of day when you’re typically not home.

Check the furnace filter

A dirty filter could reduce the air flow in your furnace. We often find that clogged filters are the culprit for why a furnace won’t kick on. If you do find that your filter is rather dirty, go ahead and change it and wait a couple hours before reassessing if you do need a service call.

How to find your filter:

The furnace filter is normally located inside the blower compartment. Where the blower is just depends on how your furnace was installed.

Common areas the filter will be:

  • In a bottom door blower compartment on the furnace
  • In a top door blower compartment on the furnace
  • A rack that is built-in on the side of the unit
  • Behind a return air grill separate from the furnace

Check the pilot light (on older furnaces)

If you have a gas furnace, you can check to make sure your pilot light is still lit. You will find the pilot light by looking in a little see-through panel on the front of the furnace door. If it’s lit, you will be able to see a flame. If it isn’t, this means there is no gas supply to your furnace. This could be due to a number of reasons, including a safety issue that has caused your furnace to shut down out of caution. If you find your pilot light has gone out, call for professional furnace service.

READ MORE: How to Light a Furnace

If your furnace is very new or highly efficient there may not be an easy way to check the pilot light yourself and a professional will need to check things out.

Check the exhaust vent

If your exhaust vent outside is blocked, it can prevent the furnace from operating. We’ve seen this happen many times after a heavy snow when the snow was deep enough to cover the exhaust pipe. Simply clear the obstructions from the pipe and the furnace should resume working normally if that was the culprit.

Check the blower motor

In order to check your furnace blower motor, peek through the plastic window on the front of the furnace. It is possible that, depending on the brand, your furnace does not have this window. If it does, know that different furnace brands may also have different light indicators for regular operation or error codes. Typically, a red/yellow/green light that is continuously illuminated or is flashing in a regular pattern indicates normal operation. A red, yellow or green light that is flashing quickly, then slowly or at other variable patterns most likely indicates an error code. Further inspection into the blower motor should be done by a professional HVAC company.

How to check the furnace power switch

furnace switch with arrow

One last area you can check when your furnace won’t start is the furnace switch. This can be on the side of the unit or mounted on the wall. This switch is responsible for the power to the furnace. If it is off, turn it back on and see if this restores proper heating operation. If it will not stay on, then it’s time to call for professional repair.

Still in Need of Furnace Repair Near Cincinnati?

We’ve gone over how to check your furnace components when the furnace won’t start. If none of these seem to solve your furnace start-up problem, then give an HVAC professional a call. If you’re in the Cincinnati, OH area, Quality Comfort Home Services would be happy to help! 


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