A wiring plan would probably help! Thanks. Although, I had a look at some last year and got very confused. I understand how the S-Plan and also the single zone X-Plan on Intergas work. The problem seemed to be getting a plan for two zones using PDHW and standard (non EPH) controls. Also, there might have been a difference in the wiring between the Xclusive and the ones which did OV. I tried really hard last year to work it out, but I have forgotten most of it.