D4
Bosch DHW NTC Sensor Circuit Fault

Boiler shows a DHW sensor circuit fault; hot water may be disabled.

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Safety Warning

This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.

If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.

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Possible Causes

Open or shorted DHW NTC, Broken DHW sensor wiring, Connector not seated on PCB, Control board sensor circuit failure

How to Fix / Troubleshooting

Safety: Isolate power and water supply to the boiler if removing any wet components.

Steps:

  • Check DHW NTC connection: Locate the DHW sensor on the plate heat exchanger or DHW outlet. Ensure the plug is fully inserted.
  • Inspect for leaks: Look for any water leaks around the DHW heat exchanger that could have damaged the sensor or wiring.
  • Test sensor and cable: With power off, disconnect the sensor and measure resistance. Also test continuity of the cable to the PCB. Replace faulty parts.

Note: If the circuit still reads open/short at the PCB with a known good sensor, the PCB will require professional replacement.

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Repair Difficulty

Medium 3/5

Required Part

DHW NTC Temperature Sensor
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