"Al" wrote in message
. 4...
Okay, here is how it works....

[snip]

Thanks - Makes sense now :-)

Simple really isn't it :-)


It turns out that the HW valve is permanently open. After cleaning the
exteriors of the valves up it looks like the HW is switched to the open
position (there's a little slider on the end of the valve). It's not clear
from the markings which is the open position, but the two valves are set
to
opposite settings.

So I guess that explains why the pump runs continuously. I think the
heating 'problem' yesterday was a red herring - We had a house full of
people, all of the lights on etc. When the pump kept running I assumed it
was a CH problem :-)

Is there any reason why the HW valve should be set differently?

If it is the same make and model as the CH valve, then no (assuming the
power was removed from it of course)

One last think I would suggest is to turn off the power to the heating
system completley (normally via a Fused Connection Unit (FCU) near the
boiler) this should stop the pump and make sure there isn't any power going
to the valve keeping it open (maybe even turn off all the power in the house
to be 100% sure someone hasnt crossed wired it somehow!)

If this still keeps the valve open and it is exactly the same make and model
as the CH one then I would say it is faulty.

Now these valves work with a little motor and a spring - when there is power
applied to the valve it opens, then when it is removed, the spring pulls the
valve closed again. The spring may have broken or come loose, but more
likley, the actual valve that rotates (just like a 1/4 turn tap) is sticking
for some reason.

You say there is a little leaver on the side - when everything is off from
the boilers FCU (pump not running!) try to manually move the lever, but
don't force it and break it! Sometimes they stick because they have been on
permanantly for weeks on end (normally because you have the HW on 24h on the
timer, and the thermostat on the side of the cylinder is set to high (too
high meaning higher than the boilers internal stat) sometimes they can be
jiggled and then they are fine - I would suggest trying this before you
change it.

BTW, the house used to be a bungalow (now extened upwards and outwards),
so
the HW cylinder and boiler are both on the ground floor - I guess that's
why it's a fully pumped system.

Sounds logical to me!

Sparks...