I currently have a Y-Plan heating system. The pump and 3-port valve are both
in the airing cuboard with the 3-port valve sitting more or less on top of
the pump. The outlets from the 3-port valve - one to the coil in the
cylinder and the other to the radiators - are horizontal, and are level with
the top indirect coil connection, about half way up the cylinder.
The 3-port valve is showing its age and will soon need replacing. I would
like to convert to an S-Plan system by replacing the 3-port valve with two
2-port valves plus an automatic by-pass. I would also like to insert some
full-bore lever valves to make it easy to isolate each component for
I cannot do this without changing the layout somewhat. There is not enough
horizontal pipe either side of the 3-port valve (to be repaced by a tee) to
insert 2-port valves. So I would like to extend the pipework by a foot or so
above the current level, tee to 2 horizontal branches, and then come down
again vertically with a 2-port valve in each vertical drop. I would, of
course, put a vent pipe with bleed screw at the hightest point.
Can anyone see any problems with this?
The fed to the coil in the cylinder doesn't really need to enter at the bottom
connector you know, so you could lift the branch from the pump higher and place
the zone valves on two different levels all together. That way you can keep the
branch to the rad' circuit where it is, and only swap round the heating coil so
it runs the other way. One TEE and a couple of elbows would do it.
Ah ha !!! With you now. So you really to make a loop that sits behind the hot
water cylinder that will also act a by-pass loop for the whole system as well
then. What orientation is the pump in? If it's standing up on end, with the
inlet and outlet vertical, then you can still take a full loop of 22 mm copper
straight up and make a big loop that sits behind the cylinder. You then take
the indirect coil from a point along the riser pipe from the pump and connect it
to the top most end of the coil the same as it is now.
With another TEE below the one for the water coil, you fit another zone valve
for the central heating loop. One more TEE will take the return from the
by-pass loop behind the cylinder back to the point where the return from the hot
tank is now.
Would that work?
- Take the flow from the boiler to the top of the airing cuboard and to the
open vent of the F&E tank.
- Tee off at the top of the airing cuopboard and take the pipe down (the
pump must be on this length half wat from the cylinder to the ceiling, as
this reduces pump niose).
- Directly after the tee insert another tee and take this to the cold feed
of the F&E tank.
- The two tees must be close together.
- The feed tee must be nearst to the pump.
- At the end of this downards length have a bend and insert the CH zone
- Tee off just before the bend and insert the DHW zone valve, then to the
top of the cylidner coil.
That is it. This is now self venting too and no need for manual air vents
and puim pnoise vastly reduced. More space for maintenance too. Insert the
pressure by-pass valve after the CH zone valve and it must be the last tee
into the boilers return. Sorted.
Use adpters for the pump, not adpters and isolation valves. Put a full bore
- The flow just before the pump
- Just after the by-pass valve after the CH zone valve
- Just after the by-pass tee on the return.
Then with 3 valves you can isolate the cylinder, zone valbe, by -pass and
I wouldn't bother. The "wet" part of a 2 port valve is usually pretty
reliable. I wouldn't be convinced that the isolation valves would be any
more so and there are 2 of those to go wrong!
Certainly, the replacement of the wet part of a 2 port valve is sufficiently
infrequently required that a drain down is not an issue.
Fair enough, but I still want full bore valves either side of the pump
rather than the existing gate valve adapters - so I still need to raise the
level of the tee above that of the existing 3-port valve. Even without
isolation valves, I still can't get 2-port valves on the horizontal pipes
either side of the tee.
So I still need to raise the pipework up higher and then come back down to
the upper inlet on the cylinder (which is about half-way up).
Is this a problem?
Another thing: IMM is telling me that the output from the by-pass valve
needs to last thing tee'd into the boiler return. Is this necessary? It
would be much easier to tee it into the HW return before it disappears under
the floorboards and joins up with the CH return somewhere or other. Is this
a problem - bearing in mind that the by-pass will only operate when both
zone valves are closed, so it can't make water flow backwards round the HW
You can get pump adapters with ball valves instead of gate valves. They
should be considerably more reliable.
Go up to the T and then put the valves on the "back down" section. Place a
bleed valve on the top of the loop. It is probably not necessary in use,
though, if sealed pressurised operation is used, as it covers a multitude of
installation sins. However you should still install the valve, in case it
does prove necessary to use it.
Just had another thought. Would it make it easier to install the DHW zone
valve on the cylinder return connection? There's no reason it has to be on
the flow side. Indeed, it will run 5-10C cooler on the return leg. The
radiator valve can still stay on the flow side or also be moved to the
return side provided no radiators have unusual return locations away from
the main trunk.
Well, your description isn't quite clear. In particular, you don't really
explain where the fill connection goes. You mention a T for the pump before
the T for the feed, but why would another T be needed? I'm hoping you mean
just use the remaining outlet from the previous T for the feed. Perhaps a
diagram would help?
In any case, there is no indication that the F&E tank pipework passes
through this location, or that the system is gravity fed, in which case,
other methods that use the space available may be required.
Finally, the system proposed requires the boiler to have secondary overheat
protection. If this is available, you may as well have combined vent/feed as
well, to eliminate pumping over problems, or better still, convert to sealed
Note that if the boiler does not have secondary overheat protection
(normally indicated by suitability for sealed/pressurised operation), then
the proposed control layout must be changed. This is because there needs to
be a direct unvalved connection between the header feed and the boiler
return that does not cross over or combine with the venting arrangements.
This is because the boiler needs a supply of quenching water to prevent it
boiling dry. Rising steam, or an automatic bypass valve would prevent such
I decided to post a couple of pictures to make clear what I'm on about!
The first one
shows the existing
layout. The flow pipe from the boiler comes up through the floor, with the
flow going up through the pump to the 3-port valve - then left into the top
coil connection and right and down to the radiators. The coil return comes
out of the bottom of the cylinder, through a gate valve for balancing, and
then disappears through the floor under the pump electrics. Somewhere under
the floor, the HW and CH returns merge into a single boiler return pipe.
The system is currently vented, although I may convert it to sealed at some
time. The boiler (Baxi Solo MK I) *is* suitable for sealed operation. The
F&E tank is in the attic directly above the airing cupboard. There is a
single 22mm pipe tee'd into the flow pipe just under the floor and running
across to the LHS of the airing cupboard, where it splits into 2 pipes which
go up the wall to the attic - not visible in the picture - 22mm vent and
The second picture
is marked up in
red to show the propsed changes, as follows:
* get rid of the 3-port valve and the 2 horizontal pipes either side of it
* extend the pump outlet pipe up higher (probably raising the pump at the
same time to get a full bore valve under it
* run 2 horizontal pipes from the top of the extended flow pipe - one going
down through a 2-port valve to the top coil connection, and the other going
down through another 2-port valve to connect into the CH flow pipe
* fit a vent at the highest point (the top right red bit)
* fit an automatic by-pass valve between the flow pipe above the pump and
the HW return - replacing the existing gate valve with a tee (I can fit a
gate valve on the inlet instead, if needed)
Moving things up like this gives me a lot more room to manoeuvre - including
space for a few full-bore isolation valves to enable component changes
Are there any glaring gotchas in my proposal?
Thanks for your interest.
Personally, I would use the automatic bypass valve to "short out" the hot
water zone valve. I would also remove the balancing gate valve. Hopefully,
this will give hot water priority and the pump overrun will dump any heat
into the cylinder. This is NOT an appropriate solution on an unvented
cylinder. It should only be considered for gravity cylinders and heat banks.
Tha't an interesting idea. Dumping a bit of heat into the HW for a few
seconds (during pump over-run) certainly wouldn't do any harm.
Presumably you are referring to unvented *cylinders*? I assume that if I
convert the *primary* circuit to unvented, that wouldn't be a problem?
It's probably a good idea to get rid of the balancing gate valve - in fact,
I'll open it right up now to see what happens. Since I've fitted a
programmable stat on the CH, I generally heat the HW when the CH isn't on,
anyway - so there's no need for any balancing.
Can you see any other problems in what I want to do - with reference to the
pictures mentioned in my earlier post? [
There is one disadvantage I can think of, though. You could possibly
overheat the water if all the TRVs are set low and the ABV starts to open. I
don't know if this would cause much of a problem in a cylinder. It would
cause none in a heat bank, as the water is supposed to be kept hot and it is
water that would have passed through anyway.
Yes, an unvented cylinder. The primary can be sealed pressurised.
Having an auto by-pass dumping heat into a cylinder is a no, no, unless. the
cylinder has a boiler high temp cut off and a hot water draw-off blending
valve. Without these, water in the cylidner may get to scalding level and
the cylinder will may get to boiler flow temperature (not a problem if a
blending valve is used).
[So what happens if you have gravity primary circulation in the HW circuit
(with no zone valve and tank stat to convert them to C-Plan systems) - as a
great number of systems still do?]
Back to the main subject, if I can't dump the bypass into the cylinder,
what's wrong with dumping it into the HW return before it merges with the CH
return, as per
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