Furnace LED shows code 33 (limit or flame rollout switch open). Blower may run continuously, burners off.

Safety first: Turn off power and gas. An open rollout switch can indicate a serious combustion problem.

• Check and replace filter: Remove and inspect the return air filter. Replace if dirty or overly restrictive.
• Verify blower operation: With power on and fan set to ON at the thermostat, confirm the indoor blower starts and moves air strongly from the supply registers. If not, the blower motor or capacitor may be failing.
• Reset manual rollout switches: With power off, locate rollout switches around the burner area. Press the red reset buttons if present. If a rollout switch was tripped, do not ignore the cause—look for signs of soot, melted wiring, or flame marks.
• Inspect supply ducts: Ensure that too many supply registers are not closed and that dampers in the ductwork are open.

If code 33 returns after resets, or if you see signs of flame rollout or heat damage, shut the furnace down and have a professional inspect the heat exchanger and venting system.