BoilerFaultCodesYour boiler is currently running a programmed self-test to check that it can safely shut down if it gets too hot.
This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.
Technical description: Test function for the safety temperature limiter (STL): The burner is switched on with maximum output until the software STL responds
What causes this fault?
This is a routine safety procedure rather than a mechanical failure. The boiler intentionally runs at maximum power to verify that the high-limit sensor can correctly detect an overheat scenario and shut the system down safely. Once the software confirms the safety limit works, the boiler will return to its normal heating mode.
DIY fix possible
Wait for the test to complete automaticallyDo not turn off the power while the test is runningMonitor the display to ensure it returns to normal operation once finished
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A boiler cover plan would cover faults like P.5 — no call-out fees, no surprises.
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