motorized valve for heating wont turn off ?

Hello,

I am looking for some advice here.

My gas central heating is not working properly.
I have a baxi gas boiler with a sunvic timer and a sunvic room temperature controller. I have only 1 room temperature controller for the whole apartment.

The timer can heat either water or rads.
The water is working fine. The motorized valve opens and closes when required.

If I call for heat on the rads - the motorized valve at the boiler inside the hot press wont stop turning around. It never stays opened or closed and the rads are heating up.

I then turned off the call for heating to the rads via the timer and set the temperature on the room to 0 but the motorized valve for the rads still wont stop turning. I checked the boiler and the rad light is not coming on.

If I remove the timer from the wall the motorized valve will still not stop turning. The only way to stop it turning is when I knock the boiler off.
Even if I switch to water only on the boiler the rad motorized valve will still turn.

Is their something I can do to eliminate if the problem is with the timer, the temperature controller or the motorized valve ?

P.S I also - turned the boiler off, set the motorized valve to the off position and turned everything back on but it made no difference.

Thanks in advance

motorised valves are not supposed to keep turning. They operate in a very limited range usually 1/4 turn to move the gate to on/off inside the brass coupling.

It's not unusual for the MV to fail especially as some dodgy plumbers locate them on the underside of the plumbing pipework which leaks and knackers the electrics.
Removing the mv cover mechanism should be achievable by a keen amateur. you can then see what's happening with the system running.

The issue will be the microswitch inside the motorised valve. The grey wire is permanently fed from the spur and the orange wire is the auxiliary switching circuit to the boiler. The grey & orange are connected inside the motorised valve via a micro switch. It will be nothing to do with a leak. They just become faulty.

You could kill the power at the spur, remove the fuse and test that all cables are dead, including neutral in case of reverse polarity. Open the cover of the MV and locate the micro switch and see if you free it. If you are handy at soldering, you can replace the micro switch purchased cheaply on-line. Failing that, you would need to replace the hold valve head.