In an earlier contribution to this discussion,
Steve wrote:

Thanks to all for the info so far.

I've had a closer look and there are 3 pipes going in to the zone
valve.
I assume one comes from the boiler, one goes to the HW cylinder (which
does have a cylinder thermostat) and one goes to the pump. There is a
smaller pipe that comes back from lower level on the cylinder and
joins the pipe going to the pump.

Is there any chance that you could take a photo of the pipework round the
3-port valve and pump - and stick it somewhere on the net, and post a link
to it here?


The electrical box on top of the zone valve only has one screw on it -
high up on the opposite end to where the cable goes in and the little
lever sticks out. I haven't tried unscrewing it yet - is this wise
with the power still on? It doesn't look like this screw would
release the electrical gubbins from the valve, but I suppose it might
give access to screws that do.


Is there any make/model information on the actuator? If you tell us that,
someone may be familiar with your type of valve.


I have fiddled with the little lever that sticks out. It was in the
central position, but if I move it to one side or the other, it seems
content to stay where I move it to.

I have also tried putting the lever to the central position, then
switching on just the heating - the lever doesn't move. Same thing
if I try putting on just the water.

Does any of this give a clearer idea of exactly where the problem
lies?

If the valve is working, it should certainly move when you change heating
selections. It's a very low geared motor though - and may take a minute or
more to move from one position to another. Are you giving it long enough?

From what you've written so far, the prime suspect is still the 3-port
valve.

One more thing you can try. Remove *all* power from the system by turning it
off at the main FCU - not just at the programmer. You should then see and
hear the valve move to the HW position under the action of the spring
return. If it doesn't, something is definitely wrong with the valve. If it
does, try running the system again - it may just be ok this time. These
valves do sometimes get confused, and need to be "re-booted".
--
Cheers,
Roger
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