Mid position valve sticks on CH, will not release

[StuartA]

Hi
I have a Drayton MA1 3-port mid position valve that sticks in the central heating position when the heating is switched on by the wall thermostat. The only way to release the the little black toggle lever on the unit is to turn off the mains power at the switched fused spur. This has to be left off for at least an hour otherwise the valve does exactly the same & sticks, leaving the radiators unbearably hot.
This has happened quite a bit over the last few years & I have replaced the synchronous motor approx 6 times but this time it didn't work. I replaced the whole unit, brass vale the lot but it stuck after about 30 mins of putting the heating back on.
I checked on the net & another suggestion was that it could possibly be the Honeywell T6360 wall stat at fault so I've replaced that & still no joy.
Now I have no idea what to try next & I'm about £80 out of pocket so here I am asking for some help/advice.
Thanks in advance.
Stu

 

[newcastle phill]

Call a heating engineer in.
It will save you grief

 

[StuartA]

Thanks Phil, think I may have to, just thought I'd give this a go on here first though.

 

[doitmyself]

I have a Drayton MA1 3-port mid position valve that sticks in the central heating position when the heating is switched on by the wall thermostat. The only way to release the the little black toggle lever on the unit is to turn off the mains power at the switched fused spur. This has to be left off for at least an hour otherwise the valve does exactly the same & sticks, leaving the radiators unbearably hot.

Follow the checks below in the order given and report results.

Turn power Off
Set HW and CH to OFF
Set cylinder stat low
Set room stat low
Turn power On
Turn CH On (Boiler should stay off)
Turn room stat up
Boiler should light and pipe from valve to rads get hot (Port A on valve)
Check boiler goes on/off when room stat turned up/down.
Leave room stat down (Boiler off)
Turn HW on (Boiler should stay off)
Turn cylinder stat up
Boiler should light and pipe from valve to cylinder get hot (Port B on valve)
Check boiler goes on/off when cylinder stat turned up/down.
Leave cylinder stat up (Boiler on)
Turn room stat up
Valve should move to mid position (pipes to cylinder and rads both get hot)
Turn cylinder stat down
Boiler should go off and restart almost immediately (pipe to cylinder should cool down but pipe to rads stay hot)
Turn room stat down
Boiler should go off

 

[StuartA]

Hi doitmyself,
I can't set the Ch Hw to off without the power on so powered it down & then set both to off. Got as far as turning the room stat up, boiler kicked in & valve stuck on CH, so didn't get far at all
I've about had enough of it now so am going to (hopefully) find a reputable local engineer to come & sort it out.
Thanks for the advice anyway.
Stu