Why Your Furnace Is Running Constantly

Furnaces run through heating cycles: you should expect the furnace in your home to turn on and off several times during an hour when the thermostat is set to supply your house with heat. These cycles last from 7 to 20 minutes on average depending on how much heat your home needs. If the furnace begins to run in shorter bursts of only 2 to 3 minutes, it’s a problem called short-cycling that you’ll need to have professionals investigate.

The opposite problem can occur: a furnace that seems to run most of the time without cycling down. This kind of “nonstop” furnace will waste money while raising the temperature of your house far higher than you want it. When you notice this occurring, don’t try to get around it by just lowering the thermostat. The furnace may have a serious malfunction, and you’ll want our help with heater repair in Colorado Springs, CO.

Why This Might Happen

As with most HVAC system malfunctions, there are multiple possible causes for a furnace that’s cycling for too long. This is one of the reasons why you want our Peak Home Performance experts on the job—we can get to the root cause quickly and make the proper repairs.

Below are some of the culprits that can cause a “runaway furnace.”

Dirty air filter

This is something you can check yourself. When the air filter for a furnace becomes excessively dirty, it restricts airflow into the HVAC system and makes it harder for the furnace to heat the house. The furnace will then run longer to try to keep up. The filter needs regular changes through the season (every 1 to 3 months), so if you haven’t changed the filter yet this winter, do so now and see if the furnace goes back to standard cycling.

Faulty thermostat

If the thermostat starts to send incorrect instructions to the furnace, it can lead to the furnace staying on much longer than necessary. A thermostat can begin to misread indoor temperatures and register the home as cooler than it is. Another possibility is an electrical problem with the thermostat that’s interfering with its communication with the furnace. Our technicians can recalibrate, repair, or replace the thermostat to correct this.

The limit switch is faulty

The limit switch registers when to shut down the furnace because the heat exchanger has gotten hot enough. This prevents the heat exchanger from overheating. If the limit switch is faulty, it may not shut the furnace off at the right time. Not only will the furnace run for too long, it could overheat.

The furnace is the wrong size

You may have a furnace that was incorrectly installed so that it’s too small to adequately heat your house. It will run for long periods as it attempts to reach a temperature that’s out of its range. This is a common problem with amateur installation, and one of the many reasons to always rely on the best HVAC professionals for any furnace job. An undersized furnace must be replaced.

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