HVACopediaAll brands · Boiler troubleshooting
Won't fire
What is going on
No power / polarity, blocked vent or intake, vent damper not rotating, tripped rollout or blocked-vent switch, open limit/operating control, thermostat (vibration, oxidized contacts, broken wire, setting), LWCO tripped (low water, foaming), flow switch open.
Check in this order
- Meter at service switch (black hot/white neutral), watch start sequence, ohm the switches, inspect flue
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Source: General HVAC service practice — verify per model. Written in our own words; check the manual for your exact model.
For licensed technicians. Gas, electrical and refrigerant work must be done by a qualified, licensed person. Shut off power and gas before servicing, never bypass a safety control, and follow the manufacturer’s manual for the exact model; it and local codes always take priority. HVACopedia is not affiliated with any manufacturer; brand and model names only identify the equipment.