Have a Vaillant ecoTEC plus 618 boiler, wired as S plan, 2 x Honeywell motorised valves, Honeywell ST6400 programmer, Honeywell wiring centre and Salus RT500RF. After the summer found had no CH which I traced to valve head which I changed, worked ok for a few hours and then packed up again, did some basic fault finding using multimeter no voltage going to valve, went back to RF receiver all ok there, checked on CH ON connection on wiring centre have 240v there when calling for heat but do not have 240v on brown wire going away to ch valve which I believe is the switched live from stat on wiring centre could this be a fault on the wiring centre, possibly cracked circuit board as it is intermittent.