Furnace part
Limit switch
The limit switch stops the burner when the heat exchanger area gets too hot, protecting the furnace from airflow failures. A limit that keeps opening means the furnace is overheating — an airflow problem, not a switch problem.
The limit is a temperature switch in the furnace's airflow path. When it opens, the burner stops while the blower continues, and the furnace restarts after it cools: the classic short cycle with a limit code.
Furnaces also carry a manual-reset rollout switch in the burner area that responds to flame rollout; manufacturers are explicit that rollout switches are never jumpered and are reset only after the cause is corrected.
Signs this part is involved
- Burner runs a few minutes, shuts off, fan continues, then relights
- Limit or overheating codes in the fault history
- Hot, dusty smell with the furnace running hard
- Trips that happen mainly on high fire or cold days
Related fault codes
- Carrier 59TP6C status code 13: limit lockout or ignition lockout
- Carrier 59TP6C status code 33: limit circuit, high-heat or ignition lockout
- Carrier 59SC6A status code 33.1: a switch has opened in the main limit circuit
Codes are documented per controller; check the model number on your rating plate before comparing. Not sure which control you have?
Related
Questions people ask
Can I replace a limit switch myself to stop the cycling?
Replacing the switch does not fix the overheating and can hide it. The switch is tested and kept if it works; the airflow cause is the repair.
Is a tripping limit dangerous?
The limit is protecting the furnace, which is the safe behaviour. The danger is the underlying airflow starvation, which can damage the heat exchanger over time.
Not sure whether the limit switch is your problem?
BC Wide diagnoses by testing, not by part swapping. Tell us the model number from the rating plate and what the furnace is doing.