Hi can anyone help we moved into a new home and the central heating is not a comi boiler , and it has just started with the probelem of when you switch to hot water only the radiators still heat up really hot even with the stat on the wall turned right down can anyone help , thanks
sounds like the actuator isn't working or the 3 port valve is sticking. This will be located just above the pump, or in the loft or airing cupboard etc.
Remove the motorised valve and select water only, and then heating only and see if the motorised valve turns, if not you need a new actuator, if it does turn, check the spindle on the 3 port valve is free to turn. Either way you'll probably need a new actuator because the motorised valve will be chewed where the spindle hasn't been turning.
It's the valve passing.... The actuator would keep the valve in water-only mode as this is the "rest" position.... As such; the actuator is fine; it's the valve itself - Probably got some sludge or debris on it stopping it from closing the c/heating side of your system off properly.
it is possible that the return side of the heating circuit joins the main return BEFORE the hot water return, meaning that some of the system will heat up back to front when the 3 port valve is positioned for hot water.