Furnace shows return temperature sensor error, heating curve control disabled

Safety: Turn off power and wait for pipes to cool.

• Locate return sensor: Find the NTC sensor on the return connection of the Hoval furnace or hydraulic module.
• Check attachment: If it is a strap-on sensor, ensure it is tightly clamped to the pipe with good thermal contact and insulated from ambient air.
• Inspect wiring and plug: Look for mechanical damage and reseat the connector on the main control board.
• Reset and monitor: Power up and clear the error. If the fault persists, replace the sensor with a Hoval-specified part.