D.118 (10) Emergency

Vaillant D.118 (10) Fault Code

Also written as D11810 — same fault.

The Vaillant D.118 (10) fault code means: your boiler has detected a communication issue with a safety sensor responsible for monitoring combustion, which prevents the unit from operating safely.. It appears on 2 Vaillant models in our database.

Act immediately

Turn off your boiler and stop using gas appliances. Call a Gas Safe engineer now. This fault can be dangerous if ignored.

Technical description: CO sensor fault number: Sensor open circuit
Typical repair cost £150-300 (including labour)

Engineer required

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

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Vaillant models that show the D.118 (10) fault code

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

Source

Vaillant D.118 (10) 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