F27 Safety switch-off — Flame detected when none should be (Flame simulation)

What does F27 mean?

The boiler has safely shut off because it detects a flame signal even when the gas valve should be closed. This can be caused by moisture on the electronics, a defective flame monitor, or a leaking gas solenoid valve.

• Moisture on the electronics
• Electronics (flame monitor) defective
• Gas solenoid valve leaking
• Electrode condition
• Earth lead to electrode issue
• Thermal fuse high resistance (MK1)

Click steps to track your progress.

1. 1

   Check the condition of the electrode and the earth lead to the electrode.

2. 2

   If the boiler goes straight to F27, and fan/pump are not running, consider the thermal fuse (requires technician).

3. 3

   Check if the gas valve is passing gas by doing a local tightness test (requires specialist tools).

4. 4

   If electrode, thermal fuse, and gas valve are okay, the PCB may be faulty (contact a technician).