BoilerFaultCodesSaunier Duval F25 Fault Code
The Saunier Duval F25 fault code means: your boiler has detected that the water temperature is rising too quickly, which usually means the water isn't flowing through the system properly.. It appears on 1 Saunier Duval model in our database.
Technical description: Maximum temperature rise slope
What causes the Saunier Duval F25 fault?
This fault occurs when the internal sensors detect the heat exchanger is getting too hot, too fast. It usually means the water is trapped or moving too slowly to carry the heat away, often caused by a failing pump or a blockage in the system pipes. Essentially, the boiler is producing heat but has nowhere for it to go, so it shuts down to prevent damage.
This fault is more common when the heating is first switched on after summer, as pump components can seize up during long periods of inactivity.
DIY fix possible
Check that all radiator valves are fully openEnsure the boiler pressure is between 1.0 and 1.5 barBleed all radiators to remove trapped air from the system
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Gas Safe Register →Saunier Duval models that show the F25 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Saunier Duval F25 fault code information on this page is sourced and cross-checked against the official Saunier Duval service / installation manuals for each affected model.
Reviewed by the BoilerFaultCodes Editorial Team · Last reviewed 27 April 2026