Furnace shows domestic hot water (DHW) sensor error on combination models, hot water unstable or not available

Safety first: Turn off power and close water isolation valves to the furnace if you will disturb water components.

• Locate DHW NTC: On Roca combi furnaces, the DHW sensor is usually clipped to the DHW plate heat exchanger or pipe.
• Check attachment: Ensure the sensor is firmly clipped and making good thermal contact with the pipe or exchanger surface.
• Inspect wiring: Follow the sensor cable back to the PCB, checking for cuts or loose connectors.
• Descale if necessary: Heavy limescale in the DHW heat exchanger can cause erratic temperatures. If water flow is reduced and temperatures fluctuate, the exchanger may need professional descaling or replacement.

Warning: Opening the DHW circuit can cause leaks if not resealed correctly. Use new gaskets and follow Roca procedures.