Strange heating problem

[John3251]

I just replaced a leaking copper cylinder on a pumped heating system, that has a Honeywell V4073A1039 Mid position valve. The hot water works fine, but the heating only works until the tank stat switches off but then works again if you set the programmer to HW off ie. then the pump cuts on and off with the room stat, so these are both ok.
I replaced the programmer but problem still exists, can this be the diverter valve?
If so why would turning the HW off fix it?

 

[stem]

Sounds like there is a problem with the valve wiring. When hot water is selected at the programmer, but the cylinder stat is satisfied (set temperature reached), it has a contact inside that switches over supplying a live to the grey wire on the motorised valve. (No live on the grey wire prevents the valve opening to the heating only position)

When hot water is switched off at the programmer another changeover switch supplies a live to the grey wire and so the heating works.

Suggest you check that the motorised valve grey wire gets a live supply from the hot water off connection from the programmer and also the cylinder stat when in the “satisfied” position.

 

[John3251]

Thanks for your answer

But would this stop the pump from even switching on when the tank stat is 'satisfied'?

 

[stem]

Yes, because you need a live on the grey to pull the valve to the heating position.

It helps if you know how the 3 position valve works, see this link.

www.diyfaq.org.uk/plumbing/plumbingpage2.html#midposition

 

[stem]

As a further tip, my guess is that the wire has pulled out of the cylinder stat when you disturbed it, or the stat contacts are not changing over properly.

 

[John3251]

Thanks for all your replies Stem

I will check these things and let you know how I get on.


Great to have such a fast & good response
Thanks again

 

[John3251]

Well I checked everything out you suggest Stem and all seems ok, so tried a new valve head, no change.
I am only seeing around 60v on grey wire once tank stat is satisfied and CH & HW selected but 240v when HW deselected, remember this is a new programmer on the original backplate so wiring has not changed and connections buzz through ok.

 

[stem]

That sounds like your problem. When the cylinder stat is satisfied, the contact should switch over and put 230/240v on the grey to keep the CH going.

Are you getting 230/240v on the common of your cylinder stat when the programmer is selecting HW on? If so sounds like your Cylinder stats not switching over.

 

[Agile]

Dont assume that ALL programmers are compatable with ALL backplates!

Tony