Boiler displays flow temperature sensor fault, burner does not start or cycles rapidly

Safety first: Isolate power before removing the boiler front cover. Electronic components are sensitive and live parts may be exposed.

• Reset the boiler: Perform a standard reset from the control panel to rule out a transient error.
• Check wiring (visual only): With power off and cover removed (if you are competent), locate the flow temperature sensor on the flow pipe inside the boiler. Ensure the plug is firmly seated and the cable is not damaged.
• Inspect for corrosion: Look for signs of water ingress or corrosion around the sensor connection. Any moisture suggests a leak that must be fixed.
• Do not bypass sensor: Never bridge the sensor terminals; this can damage the PCB and create unsafe temperatures.
• Professional testing: A Nibe technician can measure the NTC resistance at various temperatures and replace the Nibe flow temperature sensor or main PCB if out of specification.