Low Warning
Cd on Viessmann Vitodens 050-W

Your boiler has lost its connection to the remote control or internet monitoring system, so you may not be able to adjust settings via your app or external thermostat.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Monitor it

This is a minor fault. Keep an eye on it and mention it at your next annual boiler service. Reset the boiler and see if it clears.

Technical description

Communication fault Vitocom 100 (KM BUS)

What causes this fault?

This fault occurs when the boiler's main control board loses its digital handshake with the communication module responsible for internet connectivity. It is usually caused by a loose connection cable, a temporary glitch in the module's hardware, or a complete failure of the Vitocom unit itself. While the boiler will continue to provide heat based on its last known settings, it can no longer receive new instructions from your smartphone or remote thermostat.

DIY fix possible

Check that your internet router is switched on and workingEnsure the Vitocom 100 communication module is firmly plugged into the boilerTurn the boiler power off and back on again to restart the communication link

Find a Gas Safe engineer
Search the official register →

Related fault codes

BCView →CFView →D1View →

Related guides you might find useful

Boiler won't turn on — 9-step checklist

Work through these before the call-out.

Read →

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 →