Furnace Short Cycling
Quick Answer
Short cycling (furnace turning on/off every few minutes) is usually caused by a dirty filter causing overheating, thermostat problems, or a dirty flame sensor. Start by replacing your air filter - this solves the problem about 40% of the time.
Safe Checks You Can Do
- 1Replace air filter - A clogged filter restricts airflow, causing the furnace to overheat and shut down.
- 2Open all vents - Ensure supply vents throughout the home are open to allow proper airflow.
- 3Check thermostat location - Move if near heat sources, drafts, or direct sunlight.
- 4Reset the system - Turn off furnace for 5 minutes to reset safety circuits.
Likely Causes
- Dirty air filter
The most common cause. Restricted airflow causes overheating and safety shutdown.
- Dirty flame sensor
Can't detect the flame properly, causing the furnace to shut off gas shortly after ignition.
- Oversized furnace
A furnace too large for your home heats quickly and cycles off before running a full cycle.
- Thermostat issues
Faulty thermostat or poor placement can cause erratic cycling behavior.
- Blocked exhaust vent
A blocked flue triggers safety shutdown. Check for bird nests or debris.
When to Call a Pro
- Replacing the filter doesn't help
- Furnace shows error codes on display
- You suspect the furnace is oversized
- Cycling has gotten progressively worse
- Furnace is more than 15 years old
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