Hi I have a heating system with an s plan configuration. the heating works fine by itself, but recently when the hot water is turned on the heating is also on even if it is not on ( i.e. the program is off, on the programmer). so tested the zone valves and found out that when heating is boosted the heating valve opens, when turned off boost it closes, when I boost the hot water it turns both valves on! and closes them when boost if off. I've changed the programmer thinking this was at fault to no avail. any sugestions?
You don't mention which programmer you have installed? So assumed you checked the outputs of the new programmer Before wiring in the Heat On/HW On connections? Ie.. you checked the heat output was OFF when you only selected HW Boost? If the programmer is good, and the correct outputs identified and If you can physically see the valve actuators working under the conditions you describe then it would suggest the wiring between programmer and valve Live (Brown) are at fault. So you should test that the wire from the programmer "heat on" goes to the Brown wire of the heating valve. And the wire from programmer "HW on" goes to the Brown of the HW Valve. Then the important part is to ensure that when you do these 2 checks that the Brown of the opposite valve is NOT part of the circuit. The usual warning of don't play with live circuits apply, so use a continuity tester with Earth as the return path.
replaced the programmer like for like. discussed with a electrician friend and he said it could only be a faulty valve head,that the permanent live is suck. changed the head and it worked fine