25 Medium

Sime 25 Fault Code

The Sime 25 fault code means: your boiler is having trouble communicating with the temperature sensor linked to your solar water heating system, which may prevent the boiler from correctly using solar energy to heat your water.. It appears on 2 Sime 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: SOLAR S2 BOILER PROBE FAILURE
Typical repair cost £120-220 (including labour)

Engineer required

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

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Sime models that show the 25 fault code

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

Source

Sime 25 fault code information on this page is sourced and cross-checked against the official Sime service / installation manuals for each affected model.

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