F.905 High

Vaillant F.905 Fault Code

Also written as F905 — same fault.

The Vaillant F.905 fault code means: your boiler's electronic control panel is experiencing an electrical overload, which has caused it to temporarily stop talking to the heating system to protect itself.. It appears on 3 Vaillant models in our database.

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.

Technical description: Communication interface switched off. Overcurrent at the communication interface.
Typical repair cost £150-350 (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.905: 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.

Vaillant models that show the F.905 fault code

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

Source

Vaillant F.905 fault code information on this page is sourced and cross-checked against the official Vaillant service / installation manuals for each affected model.

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