Mid position valve fault?

[yiano1234]

At my mothers house we have recently found that the heating is not always working and sometimes she doesnt have any hot water. If I push the mid position valve manually it will open and remain open. (rads get hot etc). However if I then turn the room stat down I hear the mid position valve change position and the rads will cool down. Then I turn it up again and it does not open. I have to move manually again to free up.

Sometimes when there is no hot water, I have to turn the heating off (on programmer) and just let it go round the hot water for 1 hour to heat it up.

I have just changed the metal head on the 3 port, and the problem is exactly the same.

Anyone have any ideas?

 

[linkyplumb]

A wiring fault somewhere?

 

[yiano1234]

Yes, It must be a wiring fault somewhere, as I have now just changed the body section of 3 port and the fault persists.

It use to work fine, but the boiler was changed in the garage last summer. There is also a frost stat in the garage. I think the problem has only come about since then. What I don't understand is all the heating controls, programmer, pump, 3 port, wiring center were not touched in the boiler change. I guess it must be wired wrong on the boiler somewhere....