Boiler shows E18, often during DHW operation, with very hot water or sudden shutdown.

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

Scaled DHW plate heat exchanger, Faulty DHW NTC sensor, Sticking DHW modulating valve, Incorrect flow rate through DHW circuit

Safety: Risk of scalding. Run taps carefully and avoid very hot water until the fault is resolved.

Check DHW temperature setting: Ensure the setpoint on the boiler is not excessively high.
Descale aerators and shower heads: Restricted outlets can reduce flow and cause overheating. Clean or replace them.
Run at higher flow: Open the hot tap fully to increase flow and reduce temperature spikes.
Professional descaling: A technician should descale or replace the DHW plate heat exchanger and verify sensor operation.

Hard 4/5

DHW Plate Heat Exchanger

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