Boiler intermittently shows E15, especially during rapid temperature changes or after long operation.

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

Defective return NTC sensor on Thermona return pipe, Loose or corroded NTC connector, Damaged sensor cable, Faulty PCB sensor input

Safety: Isolate power and allow pipes to cool before touching.

Visual check: Locate the return NTC on the return pipe. Inspect for damage or disconnection.
Connector cleaning: Unplug and replug the NTC connector to ensure good contact.
Resistance test (engineer level): Measure the NTC resistance and compare with the Thermona chart. Replace if readings are abnormal.
PCB check: If a new sensor does not resolve E15, the PCB may be faulty and require replacement.

Medium 3/5

Return NTC Sensor

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