A supposed competent corgi registered vaillant expert said that the resistance should be that, i am only acting on advice i have been given, that is why i went down that route of questioning, after all i was told it could be one of twenty things. I feel a little trodden upon here, i have explained what the servo valve is doing and no one comments on that, just about how much of a fool i am for not taking the previous advice. The previous advice has been taken and i am responding best i can. I thought this was meant to be a helpful site, not one where everyone puts me down (it is enough for one person to say to me follow the previous advice), i get the hint and i will look again at the servo valve. i did ask if the sequence of its rise and fall of the valve was correct but no one has responded to that, i do thank Andy for his simplified advice and his lasting patiences, but was wondering if my valve is doing as it should with both demand for hot water and CH?