Low Warning
CF on Viessmann Vitodens 222-W

Your boiler is having trouble 'talking' to its internal Wi-Fi or internet connection module, which may prevent you from controlling it via apps or external thermostats.

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

Communications fault-LON communication module

What causes this fault?

This fault occurs when the boiler's main control board loses its digital connection with the internal Wi-Fi or communication module. It is usually caused by a loose wiring plug, a software glitch in the module, or a hardware failure on the communication board itself.

DIY fix possible

Turn the boiler off at the main power switch for 30 seconds, then turn it back on to reboot the electronics.Check your home internet router is working correctly and within range of the boiler.Verify that any external smart thermostats or bridges are powered on and connected.

Find a Gas Safe engineer
Search the official register →

Related fault codes

C7View →F0View →

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 →