What does 33 mean?
Furnace rollout switch has opened - flame is escaping combustion chamber.
Common causes
- Cracked heat exchanger
- Blocked flue pipe
- Failed inducer motor
- Restricted combustion air intake
Diagnostic & testing steps
- 1. STOP - Check for visible rollout damage or soot marks around burners
- 2. Test inducer motor operation and verify pressure switch hose
- 3. Check flue pipe for blockages, birds nests, debris
- 4. Inspect heat exchanger for cracks or holes
- 5. Do NOT reset until root cause is found
Tools required
- Combustion analyzer
- Manometer
- Multimeter
OEM parts & part numbers
Rollout Switch, Inducer Motor, Pressure Switch
Part numbers: LH33ZP005, HC21ZE118, HK06WC069
Safety warning
⚠️ FIRE & CO HAZARD: Rollout switch tripping indicates flame rollout — extremely dangerous. Do not operate until cause is identified and repaired.
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