Furnace attempts to start but shuts down with fan running, no ignition, flue fan may cycle

Safety: Turn off power and gas. Do not operate the furnace with the combustion cover removed.

• Check flue and air intake: From outside, inspect the Baxi concentric flue terminal for obstructions (ice, leaves, nests). Clear any blockage without damaging the terminal.
• Inspect condensate trap: Remove and clean the condensate trap and siphon. Flush with clean water and ensure the trap is refilled before refitting. Blocked condensate can affect pressure readings.
• Check pressure switch tubing: Inspect silicone tubes between the flue fan and air pressure switch for splits, kinks, or water. Replace damaged tubing and ensure correct routing.
• Test fan operation: Restore power (gas still off) and call for heat. Confirm that the flue fan runs smoothly without unusual noise. If the fan does not start or is noisy, it may be failing.

Note: Replacement of the air pressure switch or flue fan should be carried out by a qualified technician, as incorrect setup can lead to unsafe combustion.