Medium Lockout
50:0 on Viessmann Vitodens 300-W

Your boiler has failed to recognize its current control screen or operating interface and is trying to switch to an alternative control method.

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

Alternative control (automatic adjustment upon recognition of the operating interface)

What causes this fault?

This fault occurs when the boiler's internal computer brain loses its connection with the display screen on the front of the unit. The most common reason is a loose or damaged data cable connecting the two parts, or an electronic failure within the display module itself. Because the components can no longer 'talk' to each other, the boiler stops working as a safety precaution.

Engineer required

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

Find a Gas Safe engineer
Search the official register →

Related fault codes

Related guides you might find useful