BoilerFaultCodesSaunier Duval F9 Fault Code
The Saunier Duval F9 fault code means: your boiler has detected an issue with the sensor that monitors water pressure, which means it cannot verify if there is enough water to run safely.. It appears on 6 Saunier Duval models in our database.
Technical description: Water pressure sensor fault. Faulty sensor connection. Check wiring
What causes the Saunier Duval F9 fault?
This fault occurs when the boiler's internal computer loses communication with the sensor that measures water levels within the system. The most common reason is that the sensor has suffered an electrical failure or has become blocked by debris and sludge, preventing it from sending a reliable reading. Because the boiler cannot confirm there is enough water to operate safely without overheating, it shuts down as a precaution.
DIY fix possible
Check the pressure gauge on the front of the boiler; it should be between 1.0 and 1.5 bar.If the pressure is too low, use the filling loop underneath the boiler to carefully top it up.Press the reset button (usually marked with a flame or 'reset') once the pressure is corrected.
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Gas Safe Register →Saunier Duval models that show the F9 fault code
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Source
Saunier Duval F9 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