CH control upgrade: valve & circulation direction problem.


C

CliveM

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?
 
S

Set Square

In an earlier contribution to this discussion,
CliveM said:
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?]
 
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C

CliveM

Most importantly, which way should the valve be fitted, and how can I
It sounds like it's the *pump* that you need to turn round, rather than
the
valve!
Been thinking about this untill I got a reply, and came to the conclusion
that the pump should be reversed to that all the water goes in the same
direction. Was a bit worried about reversing the pumped from in case it
affected any of the TRV.

You say that you have ony 2 pipes going to the boiler - 28mm - and that
the
22mm heating circuit branches off these.
Yep, thats right.
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.
Think you are right. When the HW is on (i.e gravity) water heats ok. When CH
is on heating is OK. When HW and CH are together we get no hotwater.
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?
System worked ok before, either HW only or HW & CH. Pump not touched only
the valve put in place which seems to have affected flow.
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?]
 
S

Set Square

In an earlier contribution to this discussion,
CliveM said:
System worked ok before, either HW only or HW & CH. Pump not touched
only the valve put in place which seems to have affected flow.
Seems very odd. Maybe the HW circuit has *always* flowed the other way when
the pump is on, and maybe it doesn't matter.

Have you wired the valve *exactly* as per the C-Plan diagram in
http://content.honeywell.com/uk/homes/systems.htm ?

The only effect of the valve (provided it is open!) should be to put a
little bit of extra restriction into the HW circuit - but not enough to
matter. [It *is* a 28mm valve, isn't it?] Have you checked that, when you
are not getting hot water, the valve is actually *open* and that the boiler
is still running for the CH? I'm trying to think of how you could have
mis-wired it to make the valve close when the CH is on, but I can't
instantly see how to do this. Anyway, it worth double-checking the wiring -
and maybe getting someone else to check it too.
 
C

CliveM

System worked ok before, either HW only or HW & CH. Pump not touched
Spent more time trying to work out what is happening, then fitting the
control in the first place! - never mind good excercise up the ladder.
The only effect of the valve (provided it is open!) should be to put a
little bit of extra restriction into the HW circuit - but not enough to
matter. [It *is* a 28mm valve, isn't it?]
Yep, definatly a 28mm fitting - the bore through the valve is a bit smaller
but shouldnt be a problem as the system gives HW only which is just gravity
fed.
Have you checked that, when you are not getting hot water, the valve is
actually *open* and that the boiler is still running for the CH? I'm trying
to think of how ?>you could have mis-wired it to make the valve close when
the CH is on, but I can't instantly see how to do this. Anyway, it worth
double-checking the wiring - >and maybe getting someone else to check it
too.
Wiring OK. If HW only, the valve opens, boiler fires, pump off. If CH only,
valve closed boiler fires, pump runs, if HW&CH then Pump runs, valve open
boiler fires. - If the valve is open and boiler on there should be HW.
Seems very odd. Maybe the HW circuit has *always* flowed the other way
when the pump is on, and maybe it doesn't matter.
I think you may have got its- its always flowed the other way round and no
one noticed, even though it is a bit odd. The gravity circuit runs the
oposite way round depending if pump is on or gravity only.

From what I can make out (and I think I understand it now) through the maze
of plumbing, what happens is a follows.

When the pump is running, the CH return pumps from its 22mm into a T to the
28mm which then goes (Boiler Return ^ HW). This is resulting in 1/2 the CH
return being pumped to the boiler, and 1/2 to the HW (which then becomes the
Flow). When the HW pipes return it arrives at the 28mm T with the 22mm CH
Flow comming off. As the HW return cant move the against the pumped CH flow,
what happens is that the HW return water get "sucked off" the T piece by the
pump (i.e CH FLOW ^ HW RETURN) so CH flow is a combination of Boiler Flow
and the HW return. (or to make it simple, CH returned water is pumped as HW
flow, and HW return if then pump round the CH circuit as CH flow)

This then results in HW being passed through the cylinder from the bottom up
but is obviously pumped when pump is on.

And you wonder why I am confused about all this. Anyway this now seems to
have resulted in that we do get HW when CH on (and it must have always been
like this), but that I have just been confused over the last 3 days! I
suspect that there was a load of air in the system which caused the initial
problem. (you could hear it in the pump, and boiler cut out a couple of
times), which now seems to have cleared.

Time to put the tools away (I hope) - thanks for all your help.
 
S

Set Square

In an earlier contribution to this discussion,
CliveM said:
From what I can make out (and I think I understand it now) through
the maze of plumbing, what happens is a follows.

When the pump is running, the CH return pumps from its 22mm into a T
to the 28mm which then goes (Boiler Return ^ HW). This is resulting
in 1/2 the CH return being pumped to the boiler, and 1/2 to the HW
(which then becomes the Flow). When the HW pipes return it arrives at
the 28mm T with the 22mm CH Flow comming off. As the HW return cant
move the against the pumped CH flow, what happens is that the HW
return water get "sucked off" the T piece by the pump (i.e CH FLOW ^
HW RETURN) so CH flow is a combination of Boiler Flow and the HW
return. (or to make it simple, CH returned water is pumped as HW
flow, and HW return if then pump round the CH circuit as CH flow)

This then results in HW being passed through the cylinder from the
bottom up but is obviously pumped when pump is on.

And you wonder why I am confused about all this. Anyway this now
seems to have resulted in that we do get HW when CH on (and it must
have always been like this), but that I have just been confused over
the last 3 days! I suspect that there was a load of air in the system
which caused the initial problem. (you could hear it in the pump, and
boiler cut out a couple of times), which now seems to have cleared.

Time to put the tools away (I hope) - thanks for all your help.
Are you saying that it's now working ok?

Its not a very good idea sending "spent" CH water round the HW circuit,
because it will already have cooled a bit, so HW recovery will be slow. At
the point where the return flow from the CH rejoins (what is supposed to be)
the return flow from the HW, it might be an idea to use a sweep tee rather
than an ordinary one. If fitted with the sweep in the right direction it
would be far harder for the water to go the wrong way.

How near the boiler is the point where the circuits split? Does your boiler
have 4 connection points, two of which are currently blanked off? If so, and
if the split is fairly near the boiler, you could consider having two
totally independent circuits all the way back to the boiler with no shared
pipework. That should definitely fix the problem.

Alternatively, you could convert to a fully pumped S-Plan system. You would
need an additional, zone valve, and you would have to move the pump into the
shared bit of pipework.
 
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C

CliveM

Are you saying that it's now working ok?

Yes.
Its not a very good idea sending "spent" CH water round the HW circuit,
because it will already have cooled a bit, so HW recovery will be slow. At
the point where the return flow from the CH rejoins (what is supposed to
be)
the return flow from the HW, it might be an idea to use a sweep tee rather
than an ordinary one. If fitted with the sweep in the right direction it
would be far harder for the water to go the wrong way.

How near the boiler is the point where the circuits split? Does your
boiler
have 4 connection points, two of which are currently blanked off? If so,
and
if the split is fairly near the boiler, you could consider having two
totally independent circuits all the way back to the boiler with no shared
pipework. That should definitely fix the problem.
No boiler has 2 connections.

As it is working now (i.e there is hot water) - I will leave it as is for a
week or too - and then replumb the system.
 

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