Alpha DHW Demand / Diverter Valve Fault

Boiler does not fire for hot water but central heating works normally.

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

Faulty DHW flow sensor, Stuck diverter valve in CH position, Blocked DHW inlet filter, Faulty DHW NTC sensor

Safety: Water may be hot; take care when opening taps.

Check DHW demand indication: When a hot tap is opened, the boiler should show a DHW demand symbol. If not, the flow sensor or wiring may be faulty.
Clean inlet filter (qualified person): Isolate cold water and remove the inlet filter to clear debris.
Diverter valve operation: If the boiler fires but only heats radiators when a tap is opened, the diverter valve is likely stuck and needs attention.
Sensor test: Check DHW NTC resistance and replace if necessary.

Hard 4/5

DHW Flow Sensor / Flow Switch

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