The noise occurs at both speeds just not as loud. The open therm interface ends up doing thing same most of time, the exception being the first 15minutes as house approaches the desired temp.
I can get rid of the noise by adjusting the combi bypass, but at lower setting the bypass was opening when all the rads were on or at least most. I suppose I could try an adjust it to an ideal setting. I just thought a external bypass at the end of the 22mm pipe run would be a better solution?
I don't mind fitting a bypass valve to the pipework as I have a small amount remaining pipe work to do. I just would like to do it correctly.
