No central heating - HW only threewayvalve and tank therm

I
As per my previous post, have now has a fiddle and got some more info - yet I am still puzzled. My knowledge stops after gravity HW systems!
I am attempted to sort out a friends central heating (just moved house). Their system has conventional boiler and programmer, cylinder thermostat and three way value (Pipe in - and the Port A heating, Port B HW - Drayton Flowmaster 2)
HW is OK
When Central heating is selected only HW heats - rads are completely cold - pipe work in airing cupboard is red hot.
if I push the little lever on the 3way over from HW to CH (very hard to pushover ) and hold it then the rads get warm - when I let go again the valve moves back to HW and the rads cool.
I am guessing that it is the motor on the valve? Is this right? Could it be (or likely be) anything else? What would I need to test to find out?
If it is the motor? is this a standard part or does it depend on the valve? (in this case Flowmaster 2)
Previous advised suggested that the motor had probably burned out and would need replacing.
After removing the motor, and connecting directly to 240v I have found that the motor works OK.
There is no room thermostat fitted. I have removed the cylinder thermostat, which has three connections 1,3,4 according to info on the drayton site the thermostat connects 1 to 3 untill it cuts out where it changes over to connect 1 to 4
A test with the multimeter shows that 1 and 3 are connected, regardless of the setting or hot hot the tank/therm is this does not change. It is therefore certain that the therm needs replacing.
With the therm removed the heating does not work at all - When I connect 1 and 3 together (patch cable) the heating runs again (as you would expect). The confusing part is that if I connect 1 and 4 together (as would happen if the therm reached it set temp) nothing happens! In this case shouldnt the heating run
I suspect that someone has had a fiddle before the house was sold - as the therm was not fitted securely to the tank, screws missing and some of its wiring connection looked a touch suspect
Can anyone help?
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Sounds as if it may be wired incorrectly. Have a look at http://www.diyfaq.org.uk/plumbing/plumbingpage2.html#midposition which may shed some light on how it is supposed to work and on how it should be wired.
HTH, Roger
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Thanks for the link - I was already suspecting that it was wired incorrectly, quite how I sort out the mass of wiring Im not sure - looks like a long test with the meter!
Any other suggestions, whilst I keep on reading?
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If you're lucky, all the components (boiler, pump, 3-port valve, programmer and stats) will all be connected together via a 10-way junction box rather than having joints all over the place. Do you have such as box?
If so, have a look at http://www.sunvic.co.uk/ and navigate to Product Installation Literature, and click on the first wiring diagram link. This should show you what should be connected to what.
Roger
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There is a double socket back box with a blanking plate containig a 10 way terminal block strip with the cables running into it. Looks a bit of a jungle (and fitting tight behind the plumbing) but is a start.

thanks for the link
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John wrote:

The main FAQ contains the help you need. You should probably add a room thermostat and replace any bits that don't work. Looks like most of the bits are fine. just need to be wired up right.
--
Ed Sirett - Property maintainer and registered gas fitter.
The FAQ for uk.diy is at www.diyfaq.org.uk
  Click to see the full signature.
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Thanks for the link.
Printed off the FAQ info and will take it up with me tomorrow.I have already recommened that a new programmer and room thermostat are fitted to the system
The cylinder thermostat will def need replacing, but I just cant understand why someone would fiddled with the connections and ended up wiring it up wrongly!
Im sure that I have the info now to sort it out.

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If their ambition exceeded their ability, they may well have thought that they could fix the problem by changing the wiring. [i.e. they could have confused component failure with incorrect wiring and could have tried to "correct" it!]
Roger
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