Boiler displays return temperature sensor fault, poor modulation or lockout

Safety first: Turn off power before accessing internal components.

• Reset and observe: Reset the boiler and see if the error reappears immediately or only under certain conditions (e.g., high load).
• Visual inspection: Locate the return temperature sensor on the return pipe. Check that it is firmly clipped to the pipe and that the cable is intact.
• Check for kinks or crush damage: Ensure the sensor cable has not been pinched by the boiler casing or pipe brackets.
• Call a technician: The technician will test the Nibe return NTC with a multimeter and compare readings to Nibe’s resistance/temperature chart, replacing the sensor or PCB as needed.