Worcester 350 no hot water (only when CH is on)

[lasors]

Hello all,
We've got a fault with the DHW on our boiler, an aging Worcester 350. Two pump, no diverter valve.

CH works fine, boiler fires, pump runs. With CH off we get no hot water from the tap, the pump is not running and the boiler will not fire. Turn the tap off, turn the CH on, turn on the tap... hot water, both pumps running. Switch off the CH with the tap still running and it runs cold.

Last week we had some radiators renewed and the system was flushed. The performance of those radiators not replaced is much improved. A lot of gunk was removed and there are no cold spots anywhere any more. Obviously the boiler didn't like it so maybe the two are connected, maybe it's coincidence. Anyway...

Does anyone have any insight into the potential problem please, before I start having parts replaced?

Many thanks

 

[lasors]

Found a thread on here that suggested replacing the thermistor, which I have done, but the problem remains.

Any suggestions?

 

[Dotty]

Yes.

Read the forum rules then get a gsr in.