Boiler: Won’t fire
Won't fire on a boiler: 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.
How to fix won't fire: step by step
- Meter at service switch (black hot/white neutral), watch start sequence, ohm the switches, inspect flue
If the unit shows an error code, look it up: Bosch Boiler codes Glow Brand Boiler codes Navien Boiler codes Rinnai Boiler codes Viessmann Boiler codes
Source: General HVAC service practice — verify per model. Written in our own words as a summary; always check the original manual.
General guidance for qualified technicians. The manufacturer's installation and service manual and local codes always take priority. Aurora Star Tech is not affiliated with, endorsed by or sponsored by any equipment manufacturer; brand and model names are used only to identify equipment and belong to their owners.