broken down Britony flexiflue boiler?

I previously asked for some help on my Britony flexi flue boiler the symptons are, for some time now I have only had luke warm water although the flame seems ok, the high speed fan runs on when closing the hot tap and will only go to normal on running the cold tap, having been away for a week with the boiler switched off I have now found the high speed fan cuts in immediately when I switch on electric supply and cannot be stopped the pilot although it will ignite it goes out when I turn the nob around, so no hot water at all now, the answer from one of your experts was to change the PCB, this I have done at a cost of £147 regretfully there is no change I have tried to adjust the fan but no good has anybody any further suggestions I would very gratefull if they have thankyou David Inglis