8.4.2 High

Chaffoteaux 8.4.2 Fault Code

Also written as 842 — same fault.

The Chaffoteaux 8.4.2 fault code means: your boiler is starting to heat water but quickly shuts down the flame, meaning you will likely have cold or flickering water temperatures.. It appears on 3 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: Burner goes out on hot water demand
Typical repair cost £120-280 (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 8.4.2 fault code

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

Source

Chaffoteaux 8.4.2 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