30 - 40 High

Chaffoteaux 30 - 40 Fault Code

Also written as 3040 — same fault.

The Chaffoteaux 30 - 40 fault code means: your boiler has detected a faulty internal temperature sensor that monitors the water returning from your radiators, which prevents the system from heating effectively.. It appears on 2 Chaffoteaux 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: Central heating return thermistor faulty (open circuit)
Typical repair cost £90-160 (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 30 - 40 fault code

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

Source

Chaffoteaux 30 - 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