thanks kengas, we all know that the official engineers should know what they are doing, but if it is intermittant, and unless they have the experience to have had similar/same reports, they have no idea, Vaillant responded quickly to my e-mail, but no help, the official engineer, and i am sorry if you are one of them, fits parts in the attempt of getting it right eventually, so here i am hoping someone had the same prob, and found the answer
robbo, September 2009