Low Warning
Cd on Viessmann Vitodens 333

Your boiler has lost its connection with the external remote control or internet communication module.

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

Control mode - Communication fault Vitocom 100 (KMBUS)

What causes this fault?

This fault occurs when the boiler's main control board loses its electronic handshake with the internet or remote control module. It is usually caused by a loose connection plug or a hardware failure within the communication module itself, preventing your thermostat or app from talking to the boiler. In some cases, a brief power surge can disrupt this data link, requiring the module to be checked or reset.

DIY fix possible

Check that your internet router is switched on and functioningEnsure the Vitocom communication module is plugged in and poweredReset your boiler by turning it off and on again to re-establish the link

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