"John" wrote in message
...
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?




Sounds as if it may be wired incorrectly. Have a look at
http://www.diyfaq.org.uk/plumbing/pl...ml#midposition which may
shed some light on how it is supposed to work and on how it should be wired.

HTH,
Roger