Display shows E438; unit may not modulate or control temperature correctly.

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

Open or shorted supply thermistor, Loose wiring, Sensor not properly attached to pipe, Defective supply temperature sensor

Safety: Turn OFF power and allow system to cool.

Steps:

1. Locate supply sensor: Identify the supply water temperature sensor on the heating supply line.
2. Check attachment: Ensure it is firmly clipped to the pipe and insulated as required.
3. Inspect wiring: Confirm the connector is secure and the cable is undamaged.

If E438 remains, the sensor should be replaced by a qualified technician.

Medium 3/5

Supply Temperature Sensor

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