Furnace shows error 302, frequent short cycling, water temperature rises too quickly.

Safety: Isolate power before accessing sensors.

• Locate the flow NTC sensor: On Ariston hydronic furnaces, the flow temperature sensor is clipped to or inserted into the flow pipe leaving the heat exchanger.
• Check connection: Ensure the sensor is firmly clipped and making good thermal contact with the pipe. Tighten any loose retaining clips.
• Inspect wiring: Follow the sensor cable back to the control board. Look for damaged insulation or loose connectors. Reseat the plug.
• Descale heat exchanger (if indicated): If the unit heats up extremely fast and then shuts down, internal scaling may be restricting flow. This requires a professional to chemically flush or replace the heat exchanger.