Medium Lockout
A2:2 on Viessmann Vitodens 333-F

Your boiler is likely experiencing a communication or pump error where it is struggling to switch between heating your house and heating your hot water tank.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description

With DHW cylinder priority applicable to heating circuit pump and mixer

What causes this fault?

This fault occurs when the boiler's control system loses communication with the internal pump or can no longer control the distribution of heat between your radiators and hot water tank. The most common reason is a physical failure of the circulation pump or a loose wiring connection that prevents the main computer board from sending instructions. Even if the pump is spinning, the boiler may trigger this code if it isn't receiving the correct feedback signal from the motor.

Engineer required

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

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Related fault codes

A2View →

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