Furnace displays F11, heating stops, may be associated with domestic hot water priority models

Safety first: Turn off power and close the cold water inlet valve to the appliance. Open a hot tap to relieve pressure before disassembly.

• Clean inlet filter: Remove and clean the cold water inlet filter screen on the Saunier Duval hydraulic block. Debris here can prevent the DHW flow sensor from detecting flow.
• Inspect DHW flow sensor: Remove the DHW flow sensor or turbine cartridge. Check for limescale or debris preventing rotation or movement. Descale or replace as needed.
• Check wiring: Ensure the sensor connector is firmly seated and the cable is not damaged or pinched.
• Test operation: After reassembly, open the cold inlet valve, purge air by running a hot tap, then restore power. Check if F11 clears and DHW demand is recognized.
• Replace sensor: If the sensor does not output the correct signal (tested by a technician), replace it with a genuine Saunier Duval DHW flow sensor.