High Lockout
26 on Viessmann Vitodens 050-W

Your boiler's computer has become stuck in a repeating internal test sequence and is failing to move into its normal heating mode.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

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

Technical description

Boiler operates with continuous relay test

What causes this fault?

This fault occurs when the boiler's internal electronic controller gets trapped in a perpetual diagnostic loop during its start-up sequence. It is typically caused by a hardware failure on the main circuit board where the internal switches fail to release or communicate correctly, preventing the system from ever reaching the ignition stage.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

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Related fault codes

F2View →b7View →

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