Baxi 105e problems please help!!!!

[Mogwhy]

I had had the boiler for over 6 years now with now problems until last weekend. The CH had stopped working HW functions fine. Checked on various websites pointed towards PCB but at £90 thought I had better make sure it was this before buying a new one. I have been fortunate that my father has the same boiler so I used his PCB and was able to prove problem was PCB as all worked fine.
Purchsed a new board on Monday PCB now superseded with 5112380 board slightly different layout and instead of jumper bars the new one has dip switches. I fitted new board but all was not well CH did not start and burner ignition LED on, cleared this by resetting and satrted boiler by opening hot tap and boiler switched to HW and boiler operated when tap switched off burner went out but came back on shortly after and stayed in but no modulating occuring, boiler burner stays in until hot water switched on or I switch CH off. I thought I had a faulty new PCB and so I returned it but was unable to swop as no more in stock. Obtained second PCB from other supplier same problems exist.
Does anyone have any idea's I have all dip switches in off position as old board had no jumpers shorted out.
I am at a loss Baxi will not talk to me as I am not Corgi registered but I am an Engineer in the Gas distribution side and have a good understanding of gas valves, electrics etc.
If anyone has either encountered this problem on exchanging a PCB and has been able to resolve this problem or if anyone can suggest anything please feel free to post, all advise welcome.
Thanks in advance.