LED flashes code 13; furnace may shut down and blower may run continuously or for an extended period.

Danger: This code can indicate an overheat or flame rollout condition. Turn off power and gas to the furnace immediately if you smell gas, see soot, or suspect flame rollout. Do not bypass any safety switches.

Steps:

• Turn off power: Use the furnace service switch and breaker.
• Check air filter: Remove and inspect the return air filter. Replace if dirty or clogged.
• Inspect supply and return vents: Ensure all registers and grilles are open and not blocked by furniture or rugs.
• Locate limit and rollout switches: On Comfortmaker furnaces, the primary limit is usually mounted on the heat exchanger panel; rollout switches are near the burners. Visually inspect for manual-reset rollout switches (small red button). Only reset if you do not see signs of soot, melted wiring, or burner misalignment.
• Reset manual rollout (if safe): With power off, gently press the red reset button on any rollout switch. If it clicks, it was tripped. Restore power and observe operation.
• Monitor operation: If the code returns, or the rollout trips again, shut the system down and call a professional. There may be a cracked heat exchanger, blocked flue, or burner issue.

When to call a technician: Immediately if rollout switches trip repeatedly, if you see scorch marks, or if the furnace overheats. These are serious safety issues.