Worcester Heatslave 20/25 Pump Problem

[Sailplan]

I have noticed that the pump on a Worcester Heatslave 20/25 Oil Boiler fitted in a house I have recently purchased runs continuously, even when the heating and hot water are not being used, causing any radiators without a TRV to stay hot 24x7. The only way to turn off the pump is by setting a morning and evening schedule on the boilers front panel synchronised with my heating controller (single zone Drayton Wiser smart). Other than this, both heating and hot water appear to be working normally except that lockouts can occur on cold (sub 4 degrees C) days.

Assuming that this is not the pumps correct behaviour, I would be grateful for any suggestions on what may be at fault. An engineer who made a quick 5 min visit but didn't return on the day promised suggested one of the four relays on the control PCB (87161463010) may be faulty. Do the experts on the forum concur?

All suggestions and feedback is much appreciated.

 

[oilhead]

I would suspect a fault with the diverter valve from your description of radiators heating, but would also check that wiser is wired correctly.

 

[Sailplan]

Thanks oilhead. I thought the diverter valve and the built-in pump are typically controlled independently by the circuit board? I have checked the wiser wiring and all is ok.

 

[oilhead]

Get busy with your multimeter and follow the fault finding guide. Before you start replacing PCB's check for failed end switches in motorised valves and flow switches.