Carrier furnace Status code 13: Limit circuit lockout
Code 13 means a limit or flame rollout switch stayed open for more than three minutes, so the control locked out. It is the escalated form of code 33 and clears itself after three hours.
Applies to: Carrier 58MCB four-way multipoise condensing gas furnaces and related models using the same integrated furnace control. Bryant and Payne furnaces of the same generation use the same control and code set.
What it means
The limit circuit includes the high limit switch and the flame rollout switch, and the control watches it continuously. A brief opening produces code 33 while the blower cools things down. If the circuit stays open longer than three minutes, the control escalates to a lockout and displays code 13. It resets automatically after three hours, which produces the characteristic pattern of a furnace that works for one cycle every few hours and then stops again. That is not recovery — it is the lockout timer expiring and the same fault recurring. The underlying cause is whatever opened the limit circuit, which Carrier's own documentation directs you to code 33 to investigate.
Most common causes
- Sustained overheating from restricted airflow — a dirty filter is the most common single cause.
- A flame rollout switch open, which is a serious condition requiring manual reset.
- A blower that is not running, or running too slowly for the furnace's output.
- A restricted or blocked vent.
- Blocked filters or a restrictive duct system.
- A defective blower motor or capacitor.
- A defective limit switch or a loose connection in the limit circuit.
How to diagnose it
- Read code 33's causes as well, since Carrier's documentation explicitly refers this code there.
- Check the air filter first. It is the most common cause and the easiest to check.
- Note the three-hour pattern. A furnace that runs once every few hours and stops is displaying exactly this behaviour.
- Check whether the blower runs when the furnace fires. If it does not, overheating is guaranteed.
- Note whether a flame rollout switch is involved, since those require manual reset and indicate a much more serious condition than a dirty filter.
How to fix it
- Replace the air filter and open closed registers. This resolves a large share of limit circuit faults.
- If the cause is a flame rollout switch, stop and call a technician. Do not press the reset button.
- Blower motor faults, duct problems, vent restrictions, and limit switch replacement are technician work.
- Do not keep letting the furnace lock out and restart on the three-hour timer. Each cycle is another overheating event, and repeated overheating is what cracks heat exchangers.
Notes
The automatic three-hour reset makes this fault easy to live with and expensive to ignore. A furnace that heats intermittently through a cold spell may look like it is coping while it is repeatedly overheating its heat exchanger.