High
b1 on Viessmann Vitodens 100 Compact

Your boiler's electronic control panel is failing to communicate with the internal system, which prevents the heating and hot water from functioning correctly.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed

Call an engineer soon

Book a Gas Safe engineer within 24 to 48 hours. Your boiler may be unsafe or could break down completely if left.

What the manual says

Manufacturer manual

Communication fault – programming unit (internal)

From this model's manual
Verified against the Viessmann/Viessmann Vitodens 100 Wb1a 13kw 18kw 24kw Compact Heat Only Installation Servicing Instructions Manual installation & service manual.
Plain-English guidance below. Severity, DIY steps, costs and parts are our interpretation to help you act, not text from the manual.

Engineer required

This is a high severity fault. Stop using the boiler and call a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer
Search the official register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like b1: no call-out fees, no surprise bills.

Approved partner
Domestic Appliance Guard
Unlimited call-outs, 24/7 helpline, no price-hike promise
Get a quote →

Affiliate links. We may earn a commission at no extra cost to you.

All 19 fault codes on the Vitodens 100 Compact

Seeing a different code? Every code this model can display, in one place.

0b30386068b5E4E5F0F2F3F4F5F8F9FAFdFE

Related guides you might find useful

No hot water but heating works

Almost always a stuck diverter valve on a combi.

Read →

When to replace your boiler

7 signs repair isn't worth it anymore.

Read →

Is boiler cover worth it?

Break-even maths on monthly cover.

Read →