Display shows F1 and burner does not ignite, no hot water produced

Safety first: Disconnect electrical power and close the cold water inlet valve before opening the appliance. Allow the unit to cool.

• Check water flow: Open a hot water tap fully. If flow is weak, clean inlet filters and ensure the stop valves to the Protherm heater are fully open.
• Inspect flow sensor wiring: Remove the front cover and locate the DHW flow sensor/turbine assembly on the cold water inlet. Check the plug and wiring harness to the main PCB for damage or loose connections.
• Clean or replace turbine: Shut off water, relieve pressure, and remove the flow sensor body. Inspect for limescale or debris. Clean gently with a soft brush and descaling solution suitable for potable water. Ensure the turbine spins freely.
• Reinstall correctly: Make sure the flow sensor is installed in the correct direction (follow the arrow on the body) and that O-rings are seated properly to avoid leaks.
• Test operation: Restore water and power, then open a hot tap. If F1 remains, replace the flow sensor with the correct Protherm spare.

Warning: Do not overtighten plastic sensor housings; they can crack and leak under pressure.