Why Is My Furnace Short Cycling? Causes and Fixes
"Short cycling" means your furnace turns on, runs for a minute or two, shuts off and repeats. It wastes fuel, wears out parts and leaves the house cold. Here's what's going on.
Overheating from restricted airflow
The most common cause. A clogged filter, closed vents or a dirty blower makes the heat exchanger overheat, tripping the high-limit switch. Fix: replace the filter and open registers. If it continues, call for furnace repair.
Dirty flame sensor
A coated flame sensor can't "see" the flame, so the control board shuts off gas within seconds. Cleaning the sensor is a quick repair.
Thermostat problems
A thermostat near a heat source or with a bad wire can cause rapid cycling. See thermostat repair.
Blocked flue or pressure switch fault
If the furnace can't vent properly, the pressure switch opens and the cycle restarts.
Oversized furnace
A furnace that's too large heats the house too quickly and cycles constantly. The fix is proper sizing at replacement.
Cracked heat exchanger
A serious safety issue. Rollout switches trip when flames escape the exchanger. This requires immediate attention — call our emergency heating repair line.
Annual furnace tune-ups catch most of these problems early. For furnace not working service anywhere in Tennessee — including Chattanooga, Kingsport and Jackson — call (855) 459-5498.
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