Biasi Riva problem

[Brads]

I have a Biasi boiler (Riva Advance HE M110B.32)
Problem is that the hot water doesnt come through. The boiler switches on but the plunger from the "Primary flow switch" doesnt come on and operate the microswitch so it doesnt fire. Then the Central heating wont operate. If I switch it off and leave it 5 mins the heating will come on with no problem but as soon as I demand hot water the hot water comes through but when I turn off the hot water the heating goes off.
It all seems to revolve around the hot water as I can use the heating on and off as much as I like and it works.

Many thanks for any help.....

 

[petit_pablo]

Blocked on the HW circuit, likely to be the plate heat exchanger

 

[Brads]

Is that a big job? And where abouts is that part?

I took the 3way diverter off the top and the heating kicked back straight in, if that makes any difference to the problem/diagnosis...

 

[Agile]

The plate HE is low down at the back.

You took off the diverter valve motor!

Tony

 

[Brads]

I only lifted the diverter off to see what happened for a few seconds...

The water worked first time this morning...But I know it will fail again later..
Is the any good Plumbers around Blackburn Lancashire??