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Why Does My Furnace Keep Turning Off?

Furnaces normally cycle on and off to keep your home at a steady warm temperature. Short cycling is when it goes on and off too quickly. This can strain the system and can lead to expensive repairs if it’s not corrected. Your furnace may even fail prematurely, requiring the entire unit to be replaced.

If you’re wondering, “Why does my furnace keep turning off?”, here are a few common reasons it could be happening:

Airflow Is Restricted

Low airflow can cause your furnace to shut off. It may be due to a dirty or clogged air filter, which causes the heat exchanger to overheat. Changing the air filter every 90 days, or more frequently if you have pets or allergies, can prolong the life of your furnace. A dirty blower wheel, or a supply vent that’s blocked or closed, can prevent air from reaching the heat exchanger. Heat then builds up and the furnace shuts off as a result.

The Thermostat Isn’t Working

It could be that your thermostat is placed too close to a heat source. If it’s near an oven or in direct sunlight, false readings can cause it to turn your furnace on and off at irregular intervals. Another reason for a faulty thermostat is the batteries may need to be changed. Old wiring can also cause it to malfunction and the furnace to short cycle.

Damaged Flame Sensor

The flame sensor serves an important role in detecting a flame. If there is no flame, gas can enter your home. The sensor shuts the valve to prevent this, as no flame means there’s nothing to burn the fuel reaching the furnace. But if the sensor is dirty, covered in soot, corroded, or damaged, it can’t register the flame; even if it’s burning, the gas valve will be turned off. The system will then shut down.

Blocked Flue Pipe

The flue pipe is an exhaust vent on your roof. Being exposed, it can get clogged with twigs, leaves, dirt, and bird or animal nests. If the flue pipe is blocked, hot gases will build up and your furnace will overheat. A built-in safety feature will shut it down.

The Furnace Is Too Big for Your Home

A bigger furnace won’t heat your home more efficiently. It can heat things up too fast, making things uncomfortable and causing the unit to shut down too quickly. For this issue, the only fix is to replace your furnace with one that’s the proper size for your home.

When Should I Turn My Furnace Off?

Turning the furnace off in the summer will conserve energy. Properly shutting it down requires cutting off the electrical supply and gas line. When the weather is more consistently warm in the spring, turn off the pilot light by moving the knob to the off position. If the same electrical line supplies your AC as the furnace, don’t turn off electrical power as you’ll still need cooling from your central air conditioning system.

When to Call a Professional

If you’re asking, “Why does my furnace keep turning off?” and can’t find a reason, or resolve the matter, Black Hills Home Services has trained technicians who can help. We specialize in heating and other HVAC services in the Olympia area. When your heating bill spikes, only cold air blows, your furnace makes unusual noises, or the actual temperature and that on the thermostat don’t match, you may need furnace repair or replacement. To schedule your appointment, call us at 888-402-3514.

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