Carrier furnace Code 13 — Limit circuit lockout

What this error means

The escalation of Code 33: the limit or rollout circuit stayed open more than 3 minutes, so the board locked out. It auto-resets after 3 hours. Same cause family as 33 — overheating from restricted airflow, or a tripped rollout switch.

Symptoms

• Furnace locked out and won't retry
• Code 13 on the LED
• Often follows repeated Code 33 events

Try this first (safe DIY steps)

1. Fix the airflow first: fresh correct-spec filter, open registers, clear returns
2. Power off 30 seconds (or wait out the 3-hour auto-reset) and restore
3. If it relocks, stop resetting — repeated limit lockouts cook heat exchangers

Safety: power off before any physical intervention. Never bypass covers or interlocks — fuser areas run hot enough to burn.

When to call a technician

Recurring 13 despite good airflow = blower motor, dirty evaporator coil, or limit switch diagnosis ($150–$400 typical).