How much does it cost to fix Vaillant error code D.118 (1)?

Typical repair cost for the Vaillant D.118 (1) fault is £200-350 including labour.

D.118 (1) Emergency

Vaillant D.118 (1) Fault Code

Q: What does the Vaillant D.118 (1) fault code mean?

Your boiler has detected an internal electrical fault with a safety sensor involved in monitoring combustion, causing the unit to shut down to prevent unsafe operation.

Also written as D1181 — same fault.

The Vaillant D.118 (1) fault code means: your boiler has detected an internal electrical fault with a safety sensor involved in monitoring combustion, causing the unit to shut down to prevent unsafe operation.. It appears on 2 Vaillant models in our database.

Technical description: CO sensor fault number: Heater short circuit

Typical repair cost £200-350 (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 →

Vaillant models that show the D.118 (1) fault code

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

Source

Vaillant D.118 (1) 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 27 April 2026