How to Fix / Troubleshooting

Safety: Isolate power before removing the boiler case. Never operate the boiler with the flue disconnected or modified.

Check flue terminal: Go outside and ensure the flue terminal is not blocked by leaves, snow, or debris. Clear any obstructions.
Inspect condensate drain: Check that the condensate trap and pipe are not blocked or frozen (in cold weather). A blocked condensate line can affect combustion air flow.
Listen for fan operation: When there is a heat demand, you should hear the fan start before ignition. If the fan is silent, the fan motor or its supply may be faulty.
Air pressure tubing: Inside the boiler, inspect the silicone tubes from the fan/venturi to the air pressure switch. Ensure they are not split, kinked, or filled with water. Replace or clear as needed.
Professional testing: A technician should test the air pressure switch operation with a manometer and replace the fan or switch if defective.

Boiler shows fan/air pressure fault, burner does not ignite, fan may or may not run

Possible Causes