Ideal boiler displays F3 and will not start, fan can be heard or may not run
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.
Possible Causes
How to Fix / Troubleshooting
Safety first: Fan and flue components are part of the combustion circuit. Only a Gas Safe registered engineer should remove the boiler case or work on these parts.
User checks:
- Check flue terminal outside: Ensure the flue outlet is not blocked by leaves, debris, snow, or bird guards. Clear any obvious obstruction without dismantling the flue.
- Power cycle: Turn the boiler off at the fused spur for 5 minutes, then turn back on and reset. Listen for the fan starting (a gentle whirring) before ignition.
Engineer actions (for information only):
- Test fan voltage and speed feedback to the PCB.
- Inspect and clear any internal flue or combustion chamber obstruction.
- Replace the fan assembly if seized, noisy, or not achieving required speed.
- Check PCB output to fan and replace PCB if faulty.
If F3 remains after a reset and the flue terminal is clear, contact a Gas Safe registered engineer. Do not operate the boiler with suspected flue or fan faults.