F.431 Low

Viessmann F.431 Fault Code

Also written as F431 — same fault.

The Viessmann F.431 fault code means: your boiler is working fine, but it is failing to communicate with your smart home or external heating control system.. It appears on 1 Viessmann model in our database.

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: Normal operation in line with set values of heat generator. Communication error KNX gateway.
Typical repair cost £120-250 (including labour)

Engineer required

This fault requires a Gas Safe registered engineer. Do not attempt gas-related repairs yourself.

Find a Gas Safe engineer

Search the official register for a qualified engineer in your area.

Gas Safe Register →
Boiler cover options

Avoid the next call-out bill

A cover plan would handle faults like F.431: 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.

Viessmann models that show the F.431 fault code

Click a model for the full fault code list and model-specific repair notes.

Source

Viessmann F.431 fault code information on this page is sourced and cross-checked against the official Viessmann service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 7 July 2026