In an earlier contribution to this discussion,
CliveM wrote:

Whilst it was warm I decided to add some controls (i.e none before)
to the central heating system.

Exiting system is gravity (pumped heating). Two 28mm pipes out of the
boiler, then a 22mm pumped circuit is taken of the 28mm pipes.

To keep things simple I went with what I think is called "honeywell C
Plan". Wiring OK (after a google of this group) but I have a problem.

Before starting I put heating ok HW only, and checked which was flow &
return. I then fitted the valve on the return pipe (with the correct
flow direction A-B) was recommended doing a search and as access was
easier.

After refilling I put HW and CH on, and then noticed that the water
was trying to flow through the valve (i.e B-A) and that the pump was
therefore in the return. (i.e when the pump was on, circulation was
in the opposite direction to what gravity was running before fitting
the valve)

With the HW & CH on the house got warm and all the flow/return pipes
by the boiler but the HW coil did not heat. Putting the system to HW
only also did not work. I suspected an airlock somewhere and tried to
clear without sucess.

In the end I guessed that I must have been mistaken which pipe was
flow & return and though that I have fitted the valve in the flow. I
then drained the system again, and swapped the valve around so that
the valve was in the flow with direction (A-B). Upon refilling the
system, we now had HW/HW&CH/CH. When HW only was on, the only the HW
feed got hot, then the HW return. CH was cold. All seemed ok.

This morning, put HW only on, and I notice that the water is now
flowing in the original direction (i.e through the reversed valve
B-A) and then up the HW feed. There is also now some gravity
circulation up the CH feed (but no heat in any rad). HW is heating.

How can the water travel in opposite directions between gravity &
pumped. Is it possible that gravity flow runs either direction for
some reason?

Most importantly, which way should the valve be fitted, and how can I
solve this problem?

It sounds like it's the *pump* that you need to turn round, rather than the
valve!

You say that you have ony 2 pipes going to the boiler - 28mm - and that the
22mm heating circuit branches off these.

In HW-only mode, gravity flow will be from the top of the boiler and return
into the bottom. When you turn the pump on, the direction of flow through
the pump will determine which way the water goes round the CH circuit - all
the way back to the boiler - including through the bits of 28mm pipe which
are shared with the HW circuit. Here lies the rub! If your CH flow uses the
*bottom* connection for flow (which isn't a good idea anyway, because the
boiler thermostat will be at the top!) and the *top* connection for the
return, this will interfere with the gravity flow - and either stop it
altogether or make it go round the "wrong" way.

So make sure the pump is the right way round. Was your system ok before you
fitted the valve? Have you touched the pump during your upgrade operation?

Incidentally, I doubt whether the valve really *cares* which way the water
goes through it - but you might as well line up the flow with the arrow
while you're at it. [Unless anyone knows different?]
--
Cheers,
Set Square
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