How much does it cost to fix Saunier Duval error code 40.?

Typical repair cost for the Saunier Duval 40. fault is £250-450 including labour.

40. High

Saunier Duval 40. Fault Code

Q: What does the Saunier Duval 40. fault code mean?

The internal computer that manages your boiler has encountered a serious error and can no longer control the system, meaning your heating and hot water will not work.

Also written as 40 — same fault.

The Saunier Duval 40. fault code means: the internal computer that manages your boiler has encountered a serious error and can no longer control the system, meaning your heating and hot water will not work.. It appears on 2 Saunier Duval models in our database.

Technical description: Internal fault in the Automatic Control Module.

Typical repair cost £250-450 (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 →

Saunier Duval models that show the 40. fault code

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

Source

Saunier Duval 40. fault code information on this page is sourced and cross-checked against the official Saunier Duval service / installation manuals for each affected model.

Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026