Medium Warning
bC on Viessmann Vitodens 333

Your boiler has lost its connection with the remote control unit used to manage the heating and is currently operating in a basic backup mode.

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

Communication fault - Vitotrol remote control heating circuit A1. Control mode without remote control

What causes this fault?

This fault occurs when the boiler's main control board loses the electronic link with your wall-mounted thermostat or remote unit. The most common reason is a loose or broken communication wire, though it can also be caused by a software glitch or a failure in the remote control unit itself.

DIY fix possible

Check that the Vitotrol remote control unit is correctly seated on its wall bracket.Inspect the remote control for any dead batteries if it is a wireless version.Perform a power reset on the boiler to see if communication re-establishes.

Find a Gas Safe engineer
Search the official register →

Related fault codes

bAView →bdView →CFView →

Related guides you might find useful

Yellow or orange flame — CO safety

Safety-critical — turn off, read this.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →