3 port valve problem

[Nick Cox]

Why does my heating only work when hot water is satisfied, the motorised valve only opens when hot water is up to temp when I turn up cylinder stat valve shuts again. Worked ok for long enough wondering if its the synchron motor but it seems to open valve ok when hot water is satisfied.

 

[fixitflav]

Why does my heating only work when hot water is satisfied, the motorised valve only opens when hot water is up to temp when I turn up cylinder stat valve shuts again. Worked ok for long enough wondering if its the synchron motor but it seems to open valve ok when hot water is satisfied.

If it's a Honeywell System W or similar, with either/or diverter valve (not mid-position) that's how it's meant to work. How long is long enough? Maybe you didn't notice it all summer as CH wasn't being called.

 

[Nick Cox]

15 years plus its a mid position valve

 

[SimonG]

S plan everyday.

 

[fixitflav]

15 years plus its a mid position valve

OK, sounds like it could be an electrical problem with the valve. In case you don't have it, wiring diagrams below, showing both the overall system wiring and the valve internals. Might be worth trying clean the switch contacts. If it's not that, and it's getting the right voltages when it should, sounds like a replacement head needed.
It seems to be working as a W-plan. You could just leave it like that. I have a W-plan and I don't find the time waiting occasionally for CH due to HW preference is a problem. Maybe different if you use a lot of hot water.