BoilerFaultCodesSaunier Duval F23 Fault Code
The Saunier Duval F23 fault code means: your boiler has sensed that water is not moving through the system properly, which is causing it to shut down to prevent overheating.. It appears on 2 Saunier Duval models in our database.
Technical description: Water circulation fault. Possible pump failure
What causes the Saunier Duval F23 fault?
This fault occurs when the boiler detects a significant temperature difference between the water leaving the unit and the water returning to it, suggesting a blockage or pump failure. The most common reason is a seized or failing circulation pump that can no longer push water through the radiators and pipework. Additionally, a build-up of sludge or limescale within the heat exchanger can restrict flow enough to trigger this safety shutdown.
This fault is more common in autumn when heating is turned on for the first time after summer, as pumps are prone to seizing during long periods of inactivity.
DIY fix possible
Check that the boiler pressure is between 1 and 1.5 bar on the displayEnsure all radiator valves are fully openListen for air in the system and bleed radiators if necessary
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Gas Safe Register →Saunier Duval models that show the F23 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Saunier Duval F23 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