High Lockout
53:2 on Viessmann Vitodens 333-F

Your boiler is having trouble communicating with the external pump that circulates hot water to your radiators, meaning your heating may not turn on correctly.

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

Function relay 2: External heating circuit pump (heating circuit without mixer)

What causes this fault?

This fault occurs when the boiler's main control board loses the electrical signal required to run the external pump that moves water through your radiators. The most common reasons are a complete mechanical failure of the pump motor, a loose connection in the wiring, or a fault within the internal control board itself.

This issue is most frequently noticed during the first cold spell of autumn when the pump is required to run for the first time after being idle all summer.

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

53:1View →53:3View →

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