Boiler shows F29, flame is established then lost during operation

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

Unstable gas supply or low pressure, Blocked condensate trap causing poor combustion, Faulty ionisation electrode or cable, Flue issues causing flame lift

How to Fix / Troubleshooting

Safety: Isolate power and gas before opening the boiler. Combustion checks must be done by a qualified technician.

Steps:

Check gas supply stability and inlet pressure under load.
Inspect and clean the condensate trap and drain line to ensure free flow; a blocked trap can affect combustion.
Clean or replace the ionisation electrode and check cable integrity.
Inspect the flue for partial blockage or incorrect installation that could cause wind‑related flame instability.

After repair: Run the boiler at various outputs and confirm stable flame without F29.

Repair Difficulty

Professional Required 5/5

Required Part

Ionisation Electrode

Check Price on Amazon

We may earn a commission from links on this page.