A 40 High

Chaffoteaux A 40 Fault Code

Also written as A40 — same fault.

The Chaffoteaux A 40 fault code means: your boiler's main internal computer is experiencing a critical error, which has caused the system to shut down for safety reasons.. It appears on 1 Chaffoteaux model 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: MCU fault 2
Typical repair cost £250-450 (including labour)

Engineer required

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

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Chaffoteaux models that show the A 40 fault code

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

Source

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

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