What This Error Means

Error code 33 indicates that the manual-reset limit control, often called a flame rollout switch, is open. This is a serious combustion-safety fault that requires professional diagnosis before the furnace is operated again.

Symptoms You May Notice

Furnace will not ignite or burners shut down; code 33 displayed; furnace may remain locked out; manual-reset rollout switch is open; possible soot, abnormal flame, or excessive heat near the burner compartment.

Common Causes

Blocked or damaged venting; restricted heat exchanger; cracked or damaged heat exchanger; burner flame rollout; dirty, damaged, or misaligned burners; insufficient combustion air; inducer or draft problem; failed rollout switch.

Safe Troubleshooting Steps

1. Turn the furnace off. 2. Do not repeatedly reset the furnace or the rollout switch. 3. From outside the furnace, check only for obvious snow, leaves, or debris blocking accessible vent terminations. 4. Do not remove burners or vent components. 5. Arrange immediate professional service. 6. A technician should inspect the heat exchanger, burners, venting, inducer operation, gas pressure, combustion air, and rollout circuit.

Parts Commonly Involved

Manual-reset limit control or rollout switch; burner assembly; heat exchanger; venting system; inducer motor; gas valve; integrated furnace control.

When to Call a Technician

Call a qualified HVAC technician immediately. An open rollout switch can indicate an unsafe combustion, venting, burner, or heat-exchanger condition.

Safety Notice

Never bypass or repeatedly reset a rollout switch. If you smell gas, see soot, or observe flames outside the burner area, leave the building and contact the gas supplier or emergency services from a safe location.

Manufacturer Documentation