Strange boiler issue?can anyone explain...?

ferry

Hi all, have a bit of a strange one for you!

Just on the verge of ordering a new combi boiler to replace the old Vaillant WCW242 after it was diagnosed with pcb board issues and it just cuts out when the hot water is put on full pressure
Anyway, just realized that if I put the hot water on just on low pressure initially the boiler fires on fine,turn the pressure up once the hot water starts flowing and we have running hot water for as long as we need?
But if I put the hot water on full flow straight away it just cuts out again (ignition light comes on)
Can anyone explain why this would be and are we realistically looking at a new boiler eventually at some point anyway?
Thanks for any views on this curious one

F x

Alex1983

Is it a VCW 242 if so your boiler was a very good, but very over engineered boiler. It has lots of capillary tubes inside and the whole water section works on positive and negative pressure passing through the capillary tubes to operate the micro switches. There are four circuit boards in the boiler which for a boiler of probably 30years old is very unusual. It's difficult to say what the issue would be without being in front of it. Very common faults were restrictions in the capillary tubes stopping the micro switches from operating but I don't remember that causing lockout.

ferry

Brilliant Alex as always on the boiler issues, thanks

southcoastrgi

On face value I'd agree with Alex or a diaphragm problem