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Hello
I am just adding a zone valve to my ancient gravity fed HW circuit and I was wondering why I shouldn't also add a pump in that circuit too to make sort of a pumped C plan circuit.
I could go the whole hog and convert to S plan but the two circuits currently exit the boiler on different sides so not easy from a pipework perspective. Is there a reason why I shouldn't add an extra pump on the HW circuit to achieve full 'S-plan' functionality? i.e. pumped HW and CH independent.

I assume if I do this then the zone valve on the HW should go after the pump rather than on the return side?

I can add a picture if the description above doesn't make any sense.

Thanks in advance
Richard
 
Where in the pipe are you putting the valve?
If you put it in the wrong place it could be very dangerous!
If this is an open vented, gravity hot water, pumped heating system, it’s not as simple as installing valves and pumps.


Get a Heating Engineer in to look this over for you.
 
I think, from a safety perspective, we need to know where your open vent pipe and cold feed pipe are. Neither of these pipes can safely have valves installed on them.
 
Thanks Ric,
The fill is in the HW loop. Since this is a loop I don't think that putting a valve in one side will affect things (I know that the fill shouldn't be between any pump and valve that I install).
I haven't found a vent line, there is nothing over the header tank.

However, looking at the overall circuit I now realise that the pump is pumping into the boiler not out as I had assumed from initial inspection.
I'm confused now as I would have thought this would pressurise the whole of the HW loop and fill up the header tank?
I've obviously missed something here, any suggestions?

If it helps the house is 1960s build and I don't think it has been touched since then.
 
One set of pipes 28mm also another set 22mm and maybe a 15mm one ?
 
This is what I think I have
upload_2018-1-18_12-21-9.png
 
Yep you can't put a pump and zone valve on the cylinder side without major changes etc
 
ok, thanks. But nothing wrong with doing this though which was my original plan, i.e. two zones on CH side with auto bypass to keep flow and zone valve (no pump on HW side)?
upload_2018-1-18_12-32-39.png
 
May I ask what your planing on doing and why ??
 
sure, there is an annex in the house which is currently on the same CH circuit. I would like to split it off to another zone and give it a separate thermostat.
While I was at it I was going to put the valve on the HW to make it a bit more efficient.
 
Isn't there a citrol valve fitted on the return of the cylinder??

And then you could just zone the two heating circuits
 
I see no problem with zoning the CH side.

My understanding is that a 2-port valve could safely be fitted between the tee to the combined vent and the cylinder coil, together with a pump on the return from the cylinder into the boiler. But I suspect the OP would need to put a dedicated cold feed pipe teeing in somewhere between the cylinder coil return and the boiler return if doing this to be safe (cylinder side of the pump)?

Feel free to shoot me down, as not feeling 100% convinced myself.
 
I see Ric, so that is basically mirroring what is happening on the CH side but with the fill/vent in the middle of the valves. Sounds sensible but unfortunately there is definitely not enough space to do that with the current plumbing (fill tees right next to tank).
I think I will stick with just putting the valve on the HW for now so I can at least switch that circuit off when it gets hot enough. In a year or so it will be time for a boiler change and at that point I'll probably get rid of the tank too and go for a thermal store. Lots of fun to be had then and everything will need changing anyway.
Thanks for your help all.
 
I don't think you do see what I mean, and I'm not sure I agree with myself anyway, especially my 'cylinder side of the pump' comment which I now think is plain wrong.

What sort of valve are you intending to fit, and where? A motorised 2PortValve as on your diagram?

I don't know that putting a motorised valve on the return will allow effective gravity circulation when open. Not that I've seen it done and fail, so you may find it works perfectly well, and if so, please let us know.

A Cyltrol, (or RAVI or tapstat (I know some say you need a special pocket for the sensors on these, but both manufacturers suggest strapping the sensor to the side of the cylinder, and at least one comes with an adhesive pad for this as well) is available that is actually designed for gravity. But they are around £160 at best.

To other plumbers: if there is a combined cold feed and vent and the boiler has the high limit stat it ought to have with this arrangement, is the OP technically okay to put a valve on the return? Because I'm not sure either, now I think on it.

Because, if he can safely do that, then why not put some kind of check valve or anti-gravity valve and pump on the return on the basis that when the pump isn't running, the check valve will prevent gravity circulation? As, if it were safe to do so, it would be much cheaper than a thermo-mechanical valve, give pumped circulation, and proper control.
 
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I think I will stick with just putting the valve on the HW for now so I can at least switch that circuit off when it gets hot enough. In a year or so it will be time for a boiler change and at that point I'll probably get rid of the tank too and go for a thermal store. Lots of fun to be had then and everything will need changing anyway.
Thanks for your help all.

Surely the best thing to do is do the boiler, controls, etc changes all in 1 go this summer ......

Just saying
 
Ive recently had similar considerations when thinking of replacing an old heat only boiler with a semi gravity system.
The things you need to consider are Safety and whether there’s much point. I decided that I couldn’t vouch for 100% safety in EVERY eventuality. Also when spending money on an old system, wouldn’t you just be better off puting that money towards a new system. I mean you’re going to have to replace it all at some point anyway. plus you’re never going to get as good a performance out of an old system as a new system.
 
Thanks Ric,
The fill is in the HW loop. Since this is a loop I don't think that putting a valve in one side will affect things (I know that the fill shouldn't be between any pump and valve that I install).
I haven't found a vent line, there is nothing over the header tank.

However, looking at the overall circuit I now realise that the pump is pumping into the boiler not out as I had assumed from initial inspection.
I'm confused now as I would have thought this would pressurise the whole of the HW loop and fill up the header tank?
I've obviously missed something here, any suggestions?

If it helps the house is 1960s build and I don't think it has been touched since then.

I would consider moving the pump to the boiler flow side, fitting a 3-port or 2 off 2-port valves, to rads and cylinder. While at it, move the cold fill to the flow side, so it's boiler - open vent - cold fill - pump. Cold fill preferably under and up into the pipe, to avoid convection into the header tank. Largely eliminates "seesawing" when pump starts and stops, reducing oxygen going into the water and causing corrosion. Feed the cylinder coil from the diverter valve, and cap off the gravity hot water connection on the boiler. Need a cylinder stat, which you presumably don't have at present, and wire it all up!
I did something similar when I moved into current house 18 years ago, but I also replaced the boiler as the old one was shot. Original system had pumped return like yours, pump in the boiler room. Moved the pump to the airing cupboard next to the cylinder. Still working fine.
 
Thanks folks, I split the CH side into zones and that now works fine. The HW side is ongoing as I couldn't imagine that it was possible that the pipe could be bigger than 28mm but it was 35mm - didn't even know that existed. There wasn't enough space to put the valve where I wanted it with the reducers too so that will be done another day.
I expect that any further work will be wrapped up in the big overhaul whenever that happens. I like the idea of installing something like this monster (don't know why it is so expensive though)
MULTI FUEL UNIVERSAL THERMAL STORE - SFUTS Buy online
Once I got my head around the way it works it all sounds so much more sensible.

I'm still intrigued by the pumped return arrangement on my system. I always thought that the input to the pump should have a fixed head (from the fill/vent line) but this obviously doesn't obey that rule. Is that how they used to do it? Was there a reason?
 
I know an old plumber who says they used to say the pumps would last longer if on the cooler return, though they didn't used to be made of plastic, so I don't quite get why that would make a difference. Perhaps something to do with pump valves being potentially between the vent and the boiler?
 
One last note on this for info. Having the pump only on the CH side means that you have to split the electrics in an unusual way, normally pump and boiler are always triggered but here I have had to add a couple of relays so CH -> pump+boiler but HW-> boiler only.
Still it is basically all done now. I put the Drayton Wiser smart system on and it seems to work well.
 
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