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Why Is My Furnace Short Cycling?

Furnace short cycling is a common issue that Birmingham homeowners experience from time to time. Short cycling creates undue burden on your heating system while increasing your energy bills, resulting in performance issues and equipment damage. In our most recent blog, the heating and cooling experts at Douglas Cooling & Heating discuss the causes of short cycling and how to correct them.

What Causes a Furnace to Short Cycle?

Furnace short cycling occurs when the furnace starts up, then shuts down quickly after it starts. Typically, furnaces should run for 10 to 15 minutes per cycle. When a furnace is short cycling, a heating cycle lasts only a few minutes to half the time of a normal cycle.

Causes of Furnace Short Cycling

A furnace may short cycle for several reasons. Some of these issues can be quickly remedied by the homeowner, while others require professional repairs or even system replacement.

1. Dirty Air Filters

When the air filter is dirty, air movement through the heating system is restricted. Without proper airflow, the furnace and its internal components overheat. When high internal temperatures are detected, the furnace’s limit switch will shut down operation to protect the system and allow it to cool. This shutdown is a common reason heating cycles end sooner than expected.

Whenever short cycling is detected, the air filter should be checked first. If the filter is dirty, replace it with a fresh one, allow the furnace time to cool, and watch to see if the problem persists when the furnace resumes operation. Remember to change filters on a regular basis to protect the furnace.

2. Bad Thermostat Positioning

To properly control the heating system, the thermostat must be positioned in a spot where it can accurately sense indoor temperature. This means it must be kept away from heat sources, such as appliances or exterior doors. When the thermostat is by a heat source, it will detect heat and end a heating cycle soon after it starts. It will soon detect cold again, forcing the furnace to turn back on.

Put an end to furnace short cycling caused by poor thermostat location by enlisting your trusted technician to relocate it for you.

3. Damaged Flame Sensor

The furnace is equipped with a flame sensor that detects the presence of a flame when the gas valve is open. If it doesn’t detect a flame, it closes the gas valve to prevent a gas leak. This will shut down the furnace prematurely.

Over time, flame sensors can corrode or experience dirt buildup that interferes with flame detection. This damage can cause the sensor to misread and fail to detect the active flame, ending a heating cycle early.

The flame sensor may be salvageable through careful cleaning if dirt buildup is an issue. If corroded, the component requires replacement. Have your technician address these issues that cause furnace short cycling.

4. Exhaust Blockage

Furnaces have a flue pipe which expels combustion gases safely away from the home. If this pipe becomes blocked, the furnace can overheat. Safety controls detect high temperatures and shut off the heating cycle, causing furnace short cycling.

Check the exit opening of the flue pipe on your roof. Remove any debris, animal nests, snow or ice accumulation, or other blockage. If the blockage is not visible or reachable, have your technician inspect the furnace for a blocked exhaust vent.

5. Wrong Furnace Size

When the installed furnace is too big for the home, furnace short cycling occurs. A furnace that’s too big for your home produces excessive heat which warms the home too fast, so cycles run short. Short cycling uses excess energy and wears out equipment at a faster rate.

The only solution to an oversized furnace is to replace it with one of proper size. Work with your trusted contractor to determine the correct furnace size required by your home.

If Your Furnace is Short Cycling, Contact Douglas Cooling & Heating

Furnace short cycling is a problem that should never be allowed to persist – it burns excessive fuel and increases wear and tear to the heating system. Contact Douglas Cooling & Heating for fast, reliable furnace repair service to stop short cycling, save energy, and protect your furnace.

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