S 25 Medium

Ariston S 25 Fault Code

Also written as S25 — same fault.

The Ariston S 25 fault code means: your boiler is struggling to read the temperature of the water in your separate hot water cylinder, which may result in no hot water or an inability to regulate its temperature.. It appears on 5 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: Tank sensor open
Typical repair cost £120-220 (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 →

Ariston models that show the S 25 fault code

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

Source

Ariston S 25 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 27 April 2026