Boiler shows error 03, fan does not start or starts then stops, no ignition sequence.

Safety: Isolate electrical power before removing the boiler cover. Flue work must comply with local regulations; only qualified personnel should modify or replace flue components.

• Visual flue check: From outside, inspect the flue terminal for obstructions (nests, leaves, ice). Remove any blockage. Ensure the terminal is not covered or modified.
• Check fan operation: With the cover removed and power restored, call for heat and observe if the fan attempts to start. If the fan is noisy, seized, or does not spin, isolate power and check for debris. If the fan windings are open or the motor is stiff, replace the fan assembly.
• Inspect pressure switch tubing: Check the silicone tubes between the fan/venturi and the air pressure switch for splits, kinks, or blockages (condensate, dirt). Clean or replace tubing as needed.
• Test air pressure switch (engineer): Using a multimeter, verify that the switch changes state when the fan runs. If it does not close or opens intermittently, replace the air pressure switch with the correct Immergas part.
• Check wiring to PCB: Ensure the fan and pressure switch connectors are firmly seated on the main control board and show no signs of burning.
• Re-test: Reassemble, restore power, and run the boiler. Confirm that the fan runs continuously during ignition and that error 03 clears.