Motorised valve seems way too hot

[Doh!]

Bit of a puzzle with home heating - 18yr old 'Y' Plan system with 12 rads, one big and one small cold header tanks in loft and a hot cylinder with coil in first floor airing cupboard.
Two weeks ago heating stopped working - but hot water production still OK. For a few days following, if I moved the toggle lever on the Honeywell V4073A motorised valve from Auto to Manual it would fire up the boiler sufficient to get the rads warm - but then it would stop. I also noticed that the body/casing of said divert valve was incredibly hot ! Way too hot to touch. The valve is fitted snug up to the side of the cylinder (foam insulated) and I also have plenty of additional lagging around cylinder - including over the divert valve...so initially I thought this was the cause of high temp of outer casing.
So I bought a new Honeywell valve. Yesterday, I replaced just the motor part of the valve (not the 3 port brass and ball part) and everything returned to normal. System now correctly responds to all demands - hot water and rads all as normal. Room stat and clock all working correctly too. But....the outer casing of the new circular motor is, once again, unbelievably hot - way too hot to touch. Seems like the circular motor is running flat out the whole time - even when the boiler has not been on for hours. Is it in the process of burning up, like the previous one ?
Any ideas ?
One other clue (maybe)...when I had the old valve assembly off I manually moved the spigot shaft of the ball from side 'A' to side 'B' and back again, many times. It moves freely - spigot didn't seem stiff. When the pump was running the ball valve goes over with a thump in the pipes - as though the ball was making a good seal across the flow.

 

[Gasmk1]

On its way out could need a new head or could be struggling because valve is stiff you could just change the head and see if that cures it if it doesn't you will need to change the body. Which will mean a drain down I would advise a plumber/heating engineer to diagnose and rectify unless you feel confident enough to tackle

 

[moonlight]

When you changed the head, did the valve body spigot move easily? New top could be struggling with a sticky valve.

 

[Stigster]

With the head off the 3-port valve you should be able to move the spindle between its positions using just two fingers. It should move very easily. If it sticks then moves, feels kinda gritty or you cannot move it by finger power alone, the body of the valve is shot and the resistance is causing the motor to struggle and overheat.

 

[SJB060685]

When CH was last port of call then the motor is held open, obviously gets hot as a result

 

[Doh!]

Bit of a puzzle with home heating - 18yr old 'Y' Plan system with 12 rads, one big and one small cold header tanks in loft and a hot cylinder with coil in first floor airing cupboard.
Two weeks ago heating stopped working - but hot water production still OK. For a few days following, if I moved the toggle lever on the Honeywell V4073A motorised valve from Auto to Manual it would fire up the boiler sufficient to get the rads warm - but then it would stop. I also noticed that the body/casing of said divert valve was incredibly hot ! Way too hot to touch. The valve is fitted snug up to the side of the cylinder (foam insulated) and I also have plenty of additional lagging around cylinder - including over the divert valve...so initially I thought this was the cause of high temp of outer casing.
So I bought a new Honeywell valve. Yesterday, I replaced just the motor part of the valve (not the 3 port brass and ball part) and everything returned to normal. System now correctly responds to all demands - hot water and rads all as normal. Room stat and clock all working correctly too. But....the outer casing of the new circular motor is, once again, unbelievably hot - way too hot to touch. Seems like the circular motor is running flat out the whole time - even when the boiler has not been on for hours. Is it in the process of burning up, like the previous one ?
Any ideas ?
One other clue (maybe)...when I had the old valve assembly off I manually moved the spigot shaft of the ball from side 'A' to side 'B' and back again, many times. It moves freely - spigot didn't seem stiff. When the pump was running the ball valve goes over with a thump in the pipes - as though the ball was making a good seal across the flow.

When CH was last port of call then the motor is held open, obviously gets hot as a result

Thanks to all who replied and apologies, I don't know if I've pressed the correct 'reply' button...but just summing up all replies....I have already replaced the head, and CH/HW is working ok now (for the time being). The spigot did move the ball valve easily, by 'easy' finger pressure, across from A to B ports and back (no resistance or sticking) and also a good solid sounding "thump" in the pipework when I moved the spigot while the pump was running - which I assume indicates that the ball is making a good seal in the ports? But still, this morning, with the outer metal casing off the head, trying to touch the circular metal cover of the motor is like touching the sole plate of an iron set to 'low'- ie, it's way too hot to keep your fingers on for more than a second. Judging by the very feint whirring sound it seems like the motor is turning constantly - even though it was at least 2hrs since the boiler last fired up. I'm assuming the standard mode of operation is that the motor should only spin for a limited time - like when the pump is running ? Could it be that the head is getting a false signal from somewhere to keep spinning constantly ? If so, where could that faulty signal be coming from - the boiler, or the pump or ..?
Thanks again for your help - most appreciated.

 

[SJB060685]

It's a Y plan, that's how these work. It's not a false signal, it's how its wired internally

 

[garygvl]

as previously said the only time that motor wont get hot is in the summer months when you have no heating on and it doesnt have to do anything. during the winter months its most likely that motor will be in mid position or full heating position with the motor energised and the spring return trying to pull it back to hot water position. It's the drawback of a 3 port mid position valve. If , which is most likely, the last demand of the day is heating that motor will be powered up all night till the morning then is only likely to go back to mid position to do heating and water at the same time. It is possible for that motor to be powered up for the entire heating season. Its told what to do by the programmer, room stat and cylinder stat not by the boiler or the pump