8 04 Medium

Ariston 8 04 Fault Code

Also written as 804 — same fault.

The Ariston 8 04 fault code means: your boiler is signalling that an additional electronic control module, required for managing specific heating zones or complex setups, has not been detected or is not communicating correctly.. It appears on 3 Ariston models in our database.

Book a service

This fault should be looked at by a Gas Safe engineer within the next week or two. It may get worse if left.

Technical description: Decoupling Clip-In required (see note)
Typical repair cost £150-250 (including labour)

Engineer required

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

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Ariston models that show the 8 04 fault code

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

Source

Ariston 8 04 fault code information on this page is sourced and cross-checked against the official Ariston service / installation manuals for each affected model.

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