05
Immergas
Flue System / Fan Speed Control Fault
Boiler shows error 05, will not start, display may indicate fan or flue fault depending on model.
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Blocked or incorrectly installed flue, Faulty fan speed sensor (Hall sensor), Loose fan connector on PCB, Control board fan driver fault
How to Fix / Troubleshooting
Safety: Turn off power before removing the casing. Flue inspection and modification must be done by a qualified installer.
- Check flue routing: Verify that the flue length, bends, and terminal type comply with Immergas installation limits. Excessive length or incorrect components can cause fan speed errors.
- Inspect flue for blockage: Check for water accumulation, collapsed inner flue, or foreign objects. Rectify any obstruction and ensure correct slope for condensate drainage.
- Check fan connector: Ensure the multi-pin connector from the fan to the PCB is fully engaged and free from corrosion or heat damage.
- Test fan speed sensor (engineer): Using the service manual, measure the feedback signal from the fan tachometer to the PCB. If no signal is present while the fan runs, replace the fan assembly.
- PCB diagnosis: If the fan and wiring are confirmed good but the boiler still reports fan/flue error, the control board may be defective and require replacement.
- Final verification: After repairs, run the boiler at various outputs and confirm stable fan speed and no recurrence of error 05.
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Repair Difficulty
Hard
4/5
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