F7 appears, water temperature unstable or unit shuts down shortly after ignition

Safety first: Disconnect power and allow the heater to cool.

Steps:

• Locate primary NTC: On Saunier Duval water heaters, the primary NTC is usually clipped to the primary heat exchanger or inserted into a pocket on the flow pipe.
• Check connection: Ensure the NTC plug is fully inserted into the PCB and that the sensor clip is tight on the pipe or exchanger.
• Inspect cable: Look for cuts, burns, or crushed sections in the NTC cable. Repair or replace as needed.
• Replace NTC if suspect: NTC sensors are relatively inexpensive. If in doubt, replace the primary NTC with a genuine Saunier Duval part.

Warning: Do not run the heater with the NTC disconnected or bridged. This disables temperature control and can cause overheating.