Display shows A7; water temperature reading is erratic or clearly wrong (e.g., shows 80°C when water is cold).

Safety: Turn off power to the heater before accessing internal components.

• Locate DHW sensor: On Junkers gas water heaters, the DHW NTC is usually clipped to the outlet pipe or inserted into a sensor well near the hot water outlet.
• Check wiring: Inspect the two-core cable from the sensor to the control board. Look for cuts, melted insulation, or loose plugs. Reseat the connector on the PCB.
• Clean sensor area: If accessible, remove limescale around the sensor pocket or pipe using a descaling solution suitable for copper/brass. Do not use sharp tools that may puncture the pipe.
• Measure resistance (advanced DIY): With the unit powered off and sensor disconnected, measure resistance with a multimeter. Compare to the Junkers service chart (e.g., ~10 kΩ at 25°C). If readings are far off, the sensor is defective.
• Replace if needed: If the sensor is clearly faulty, replace it with an original Junkers DHW NTC sensor. Refill and bleed air if the sensor is in a wet pocket.