Why Your Furnace Clicks but Won’t Start
A clicking furnace usually means the ignition sequence is trying to start but failing. The system attempts to ignite the burners, clicks, and then shuts down for safety. This cycle may repeat several times before the furnace locks out completely.
Most causes are related to ignition, sensors, or airflow restrictions.
Common Causes of a Clicking Furnace
1. Dirty or faulty flame sensor
The flame sensor detects whether the burner has ignited. If it’s dirty, the furnace will click repeatedly but never start.
2. Igniter failure
A cracked or worn igniter cannot heat up enough to light the burners.
3. Gas supply issues
If the gas valve is off or pressure is low, the furnace cannot ignite.
4. Clogged air filter
Restricted airflow can cause the furnace to overheat and shut down before ignition.
5. Faulty limit switch
If the furnace overheats, the limit switch prevents ignition for safety.
6. Draft inducer motor problems
If the inducer motor cannot create proper airflow, the furnace will not ignite.
How to Fix a Furnace That Clicks but Won’t Start
1. Replace the air filter
A clean filter restores airflow and helps prevent overheating.
2. Check the thermostat
Ensure it’s set to Heat and the temperature is above the room temperature.
3. Inspect the furnace for error codes
Most furnaces have a diagnostic LED that flashes a code indicating the problem.
4. Listen for the inducer motor
If you don’t hear it running before the click, the furnace may not be venting properly.
When to Call a Professional
Call for service if:
- The furnace clicks repeatedly without starting
- The igniter is cracked or not glowing
- You suspect a gas supply issue
- Error codes indicate ignition or sensor failure