hot water won't turn off

[Bradley31]

Hi All
We have an oil fired Boiler, Tank in the loft and Hot Water tank in the airing cupboard with a Honeywell ST9400A control and HCW80 and HC60NG remote thermostat.
For a while the Hot Water was not coming on. We had to fire up the Heating if we needed Hot Water.
I swapped the motorised head of the valve from the Heating to the Hot Water and it worked fine, so i thought i would buy a new synchron motor. I have just fitted the new motor but now the Hot Water won't switch off. When the power is on the MV activates and closes the switch which then switches the Hot Water on even though all of the controls and HC60NG are off. When i turn the power off the valve does close (and when i have turned it by hand i can feel the valve moving inside) so i don't think it is ceased open. Is it a wiring issue? or the Tank Thermostat? (i have turned the thermostat on the tank down but it has no effect. I can hear the click at over 70 degrees even though its only set to 55)
I am at a loss of what to try next. Should I keep it turned off for now?
Any help is much appreciated.
thanks

 

[Bradley31]

Could you run a new wire from the ufh manifold to upstairs where the wiring centre is ?

It’s a long way through a few rooms and ceilings

 

[ShaunCorbs]

It’s a long way through a few rooms and ceilings

That’s why I think they’ve done it the wrong way would need a new 6 core running back