On Mon, 4 Jan 2021 20:30:11 +0000, bert wrote:

The Honeywell Motorised valve controlling the CH is sticking in the Open
position so the heating is running continuously.
In this condition there is no resistance when moving the manual lever on
the head.

If I thump it a couple of times the valve moves and closes and switches
off the boiler/pump. If I then try to move the manual lever resistance
comes in when about half way across.

When hall thermostat switches on again the valve will work correctly and
may switch off and on a couple of times but then sticks open again.

So am I going to have yet another lesson in Sods Law or will I be lucky
and find its only the motorised head that needs replacing?
One of mine went like this and it was just the gear mechanism in the
head that had worn and was jamming. A replacement head fixed it, but I
waggled the spindle on the valve body a few times just to check it was
moving freely.
You can get a Honeywell compatible head for quite a lot less £££s,
I'll see if I can find a link, but someone else might know.