Boiler displays D5, may not respond correctly to external controls or sensors.

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.

Possible Causes

Incorrectly wired external sensor (e.g., outdoor sensor), Faulty sensor, PCB input fault

Safety first: Isolate power before working on low-voltage control circuits.

Engineer steps:

Check wiring of any outdoor temperature sensor or external controls connected to the boiler; ensure correct terminals and polarity.
Measure resistance of the external sensor and compare with manufacturer data.
Temporarily disconnect the external sensor to see if boiler reverts to normal operation.
Replace the faulty sensor or repair wiring as needed; if issue persists, test/replace the PCB.

Medium 3/5

Outdoor Temperature Sensor

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