Boiler shows D1, may indicate a problem with the pump or flow through the boiler.

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

Seized pump, Airlock in pump, Blocked system filter or bypass, Faulty pump speed control

Safety first: Isolate power and allow system to cool before working on the pump.

Engineer actions:

Check the pump for operation by feeling for vibration when the boiler calls for heat.
Remove the pump head and check the rotor spins freely; free it if stuck or replace the pump head.
Bleed air from the pump via the bleed screw and from high points in the system.
Inspect any system filter (e.g., Worcester Bosch Greenstar System Filter) for blockage and clean as required.
Verify correct setting of the pump speed or modulation via the PCB.

Hard 4/5

Primary Circulating Pump

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