Medium Lockout
72:1 on Viessmann Vitodens 300-W

Your boiler is struggling to accurately measure the temperature of the water being heated for your taps, causing it to shut down while filling your hot water cylinder.

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

OFF during DHW loading to set value 2

What causes this fault?

This fault occurs when the temperature sensor inside your hot water cylinder sends an incorrect or interrupted signal to the boiler's control board. The boiler shuts down as a safety precaution because it can no longer accurately monitor how hot the water is getting inside the tank. The most common reason is a failing sensor or a loose connection in the wiring leading from the cylinder to the boiler.

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

72:2View →

Related guides you might find useful

No hot water but heating works

Almost always a stuck diverter valve on combis.

Read →

Boiler keeps cutting out

Lockout fault with a reset-needed pattern.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →