BoilerFaultCodes.com
0 0. High Lockout

Your boiler has detected a flame signal when it shouldn't be there, which has caused it to shut down for safety purposes.

Call an engineer soon

Book a Gas Safe engineer within 24–48 hours. Your boiler may be unsafe or could break down completely if left.

Technical description: Flame simulation: Check ionisation probe (distance 3 - 4 mm).

What causes this fault?

This fault occurs when the boiler's internal sensor detects a flame signal at a time when the burner should be completely off. The most common reason is a faulty or contaminated sensing probe that is sending an incorrect electrical signal to the main control board, though it can also be caused by moisture on the internal electronics. For safety, the boiler will immediately shut down to ensure that gas is not flowing when it shouldn't be.

This fault is more frequent during periods of high humidity or heavy rain, as internal dampness or moisture ingress can cause the sensitive electronics to misread electrical signals.

Typical repair cost £120-250 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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