BoilerFaultCodesSaunier Duval F8 Fault Code
The Saunier Duval F8 fault code means: your boiler's temperature sensor for the hot water storage tank has developed a fault, meaning the system cannot safely monitor or heat your hot water.. It appears on 5 Saunier Duval models in our database.
Technical description: Tank thermistor fault
What causes the Saunier Duval F8 fault?
This fault occurs when the sensor responsible for monitoring the temperature in your hot water storage tank fails to send a reliable electrical signal to the boiler’s control board. The most common reason is the internal degradation of the thermistor or a loose connection in the wiring, which prevents the boiler from knowing how hot the water is. For safety reasons, the system shuts down hot water production to prevent potential overheating.
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 →Saunier Duval models that show the F8 fault code
Click a model for the full fault code list and model-specific repair notes.
Source
Saunier Duval F8 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