Hi everybody. Got a strange problem with our central heating that I'd like to get sorted before the winter. I'm posting in 'Electrical' because I believe it's a wiring problem rather than component failure or anything to do with the heating pipework. The issue is the hot water cannot be turned on without the heating. It can work the other way around though. i.e. you can turn on the heating by itself without the hot water. The obvious issue here is that you might want only hot water when the house doesn't have to be heated for whatever reason. Something which makes me suspicious about the wiring is that the H/W and C/H sides on the programmer have been reversed. You can see somebody has written on the cover to show the controls have changed sides! That's no good! I've taken off the junction box cover and traced all the wires. I've made a wiring diagram to try and help me understand the setup. My suspicion is the little jumper wire connected along the top in the junction box linking terminals 5, 6 and 8 is a potential problem. It has the effect of connecting the C/H thermostat to pin 3 and pin 4 on the 3-way valve and probably joining 3 & 4 on the valve so they effectively do the same thing. Anyone at a sufficient level of understanding of these systems to see any problems? I've got a diagram from the manufacturers website which looks as close as I can see to what I should have. We have the two-wire room thermostat and no tank thermostat.