Unit shows E05 and shuts down; temperature rises rapidly when burner runs.

Safety: Isolate power before accessing internal wiring or sensors.

• Locate DHW sensor: On Weishaupt water heaters, the domestic hot water (DHW) NTC sensor is usually clipped to or inserted into a sensor pocket on the DHW outlet or plate heat exchanger.
• Check connections: Inspect the sensor plug and wiring harness for corrosion, loose pins, or damaged insulation. Reseat the connector firmly.
• Measure resistance: With power off, disconnect the sensor and measure its resistance with a multimeter. Compare to the Weishaupt resistance/temperature table. A sensor reading open circuit or shorted must be replaced.
• Descale sensor pocket: If the sensor is in a pocket, remove it and check for heavy scale or sludge. Clean the pocket carefully and reinsert with thermal paste if specified.
• Control board check: If a known-good sensor still gives E05, the control board input may be defective and should be tested/replaced by a technician.