Valve problem help please?

[goooba769]

Just wondering if someone can shed a bit of light on a problem a friend has.
He has a closed system with airing tank expansion cylinder, etc and there is a three way motorised valve which allows heating system to heat cylinder(I think thats what its for!). When he turns the heating on to get hot water this valve initially opens but then closes and he has to manually open it to get hot water.
Can anyone give me some pointers?
Is it a faulty valve in which case can you just remove the mechanism on top of the valve and replace or do you think there is a signal fault from the boiler?
Any help or experiments would be a great help

 

[goooba769]

Come on, dont you all go quiet on me

 

[longdogs]

I'm not an expert on this but I think you can just replace the electrical part which doesn't involve draining down etc.

 

[Agile]

Its worse that the blind leading the blind!

Without stating the make and model of the valve its impossible for those who do know to answer!

Tony