Boiler shows F27 and locks out, sometimes with smell of gas at flue

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

Moisture or contamination on ionisation electrode, Faulty PCB flame detection circuit, Incorrect earth connection, Gas valve leaking slightly when off

How to Fix / Troubleshooting

Safety first: Turn off power and gas. If you smell gas, ventilate the area and do not operate electrical switches.

Steps to check:

Inspect the ionisation electrode for moisture, soot, or damage. Clean and dry as needed.
Check the boiler earth connection is secure and continuous.
Reset the boiler. If F27 persists, a professional must test for gas valve tightness and PCB integrity.

Warning: A leaking gas valve is dangerous and must be replaced immediately by a qualified engineer.

Repair Difficulty

Professional Required 5/5

Required Part

Ionisation Electrode / Gas Valve

Check Price on Amazon

We may earn a commission from links on this page.