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Furnace Short Cycling (Turns On and Off)

Furnace starts and stops every few minutes. Common causes, filter facts, and what a technician checks.

Safe things to check

• Check the air filter. ENERGY STAR says to check the air filter every month, change it if it looks dirty, and change it at least every 3 months. A dirty filter slows airflow, makes the system work harder and can lead to early failure. (Source: ENERGY STAR (U.S. EPA))
• Make sure supply and return vents are open and not blocked by furniture.

Stop here

Do not bypass safety switches. Furnaces shut themselves off when a safety check fails, and that can point to a venting or heat exchanger problem. Carbon monoxide is odorless and colorless. Gas and oil furnaces can produce it. Common symptoms are headache, dizziness, weakness, upset stomach, vomiting, chest pain and confusion, often described as flu-like. The CDC says to have the heating system serviced by a qualified technician every year. (Source: U.S. Centers for Disease Control and Prevention)

What a technician checks

ENERGY STAR says a dirty burner or cracked heat exchanger causes improper burner operation and less safe operation. A technician checks the flame sensor, airflow, venting and the heat exchanger. (Source: ENERGY STAR (U.S. EPA))

Typical cost

Angi: flame sensor $150 to $250; blower motor repair $150 to $450; heat exchanger work up to $1,500. (Source: Angi) National figures; not a quote.

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