2 pumped c/h system


Postby morris minor » Sun Jan 11, 2009 2:29 pm

Hi, my daughter has just bought a house that has a oiled fired 2 pumped c/h system with no thermostats what so ever fitted, the only meens of control was on, low, high & off. I have since put rad stats on all the rads ( it does have the usual time selector switch i/e h/w-c/h time and so on). I would now like to fit a cylinder stat and wire it up to the pump that controls the hot water, will that create any problems. I have never come accross a system with 2 pumps before it ussually is controlled by motorised valves or am I living in the past and that tech has moved on since the 60's :oops:
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Postby morris minor » Fri Jan 16, 2009 9:05 pm

has no body got any answers to my question above
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Postby plumbbob » Sat Jan 17, 2009 12:09 pm

The reason nobody has been able to answer your query is because you have an unusual system. It is impossible to offer any advice without having any information about how it is designed and apart from telling us it has two pumps, you have not given us anything else to help with a diagnosis.

The rule of thumb for anyone posting here is the more information you give, the more likely you are to get a reply.
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Postby Dave From Leeds » Wed Jan 21, 2009 10:50 am

The first thing you need to check is whether your daughter's hot water cylinder is directly or indirectly heated. Then check whether the pump that you said controls the hot water is in a pipework circuit that includes the boiler. It may be that it simply circulates water round the system that feeds the hot taps to prevent delays due to hot water coming from the cylinder displacing a slug of cold water from the pipework. If the pump's pipe circuit does not include the boiler, switching it off via a cylinder stat will give no control over the water temperature. In such a case it may slow down or even stop the flow of hot water to the taps. Armed with the information collected, it should then be possible to ascertain how to incorporate a cylinder stat into the system.
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Postby morris minor » Thu Jan 22, 2009 5:04 pm

Hi Dave from what I can make out (as access to the pipe work is very limited) first of all the flow for the c/h is feed from the boiler using 28mm pipe with 5 out lets on each from the manifold, but someone has fitted two extra rads direct from the flow and return befor the manifolds, making it 7 rads in total. The hot feed for the cylinder is fed as usual from the flow and return tappings on the boiler with a pump on the flow just befor the cylinder i/e above it in the loft. the cylinder is an indirect one and is fed from a cold water tank in the loft. The programer operates the h/w when switched to hot water and the c/h is controlled when switch moved to c/h. The pump looks like a newish installation and not done on the initial fit during the c/h being installed 9 years ago. Both the pumps are in the loft space and the pipe work to the rads is via 6mm pipe. And its a oiled fired system
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Postby Dave From Leeds » Thu Jan 22, 2009 7:56 pm

Can the central heating be run without the hot water being on with the present set-up? From the way you've just described it I suspect not. If I'm correct here, I think you'll probably need to install a motorised valve in the hot water circuit from the boiler. If you simply put in a cylinder stat wired to stop the hot water pump on satisfaction, the indirect heating system for the cylinder may continue to gravity feed through the pump. So a cylinder stat which will close the motorised valve as well as stopping the hot water pump may well achieve what you require. Good luck
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Postby morris minor » Fri Jan 23, 2009 2:05 pm

yes it can!! if only the selector switch is set to c/h, there are 2 sliding levers. its a Honeywell ST699/ST799 programmer
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Postby Dave From Leeds » Fri Jan 23, 2009 11:08 pm

Hi Morris,

I'm a bit lost now. If you can select CH only without the HW slider switch going with it, therefore allowing the central heating to be on without heating the water, something must be preventing the water from heating as a gravity system This would normally be achieved I believe by incorporating a motorised valve. However, if there definitely aren't any in the system, it may be that the position of the hot water pump above the cylinder could be achieving this. In that case possibly your original idea of fitting a cylinder stat configured to control this pump may do the trick. I guess you've nothing to lose by trying it. Please note however that I'm no more of a plumber than you are, just a DIYer. One thing that confuses me is why the central heating pump would be in the loft. Where's the boiler?
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Postby morris minor » Sat Jan 24, 2009 9:35 pm

Hi Dave, answer to the question about the boiler, its in what was once the garage now converted to a lounge with a section of it partitioned off to make a utillity room.and as for the pumps like i said they are in the loft space right down near the roof meets the walls in other words you have to lie on your belly to get at them. Not an ideal place. I did serve my time as a GAS Board fitter (NWGB) in 1960 (town gas) but in 1965 I joined the post office telephones and became a telephone engineer, and retired in 2000. so anything that i learned with the gas board is way out of date
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Postby morris minor » Sat Jan 24, 2009 9:40 pm

Dave I forgot to mention micro bore was only just started to be used as a system just as I left so I am not fimillar with the workingsof it other than i have it in my house.
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Postby Dave From Leeds » Sun Jan 25, 2009 1:13 am

Hi Morris,
Further to my last post, a simple way to check whether a cylinder stat wired into the pump would stop the water from heating would be to disconnect the electrical supply to the hot water pump. However, the limited access might make this difficult at the pump itself. If you are confident enough to locate the feed to the pump at the programmer, you could disconnect it there. You'd obviously need to turn off the power to the whole system to do this, then you'd need to reset all the on & off times on the programmer since they would revert to the factory preset ones. As someone with an inquisitive mind, I like experimenting like this. Another thing, does your forum name mean you've got one of those classic cars?
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Postby morris minor » Sun Jan 25, 2009 11:17 am

Hi Dave my secrete is out then :D yes I am almost finished retoreing a 948cc 2 door 1960 black saloon and I am the 5th owner the first two being father (Reverend Rowlands) then his son. And my run about is a 1098cc 1962/3 Maroon 2 door and I am the 5th owner of that. I seem to have a passion for being 5th owners the original owner being a sunday school teacher of a friend of ours in Menia Bridge (Anglesey). Now back to the original subject, pump vs cylinder stat, I am going to give it a try by wiring it into the programer and pump, :!: I think the original C/H installation was done in 1998 by by a chap who worked in Wylfa Power Station :!: no comment :wink:
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Postby morris minor » Sun Jan 25, 2009 8:02 pm

RE pumps, both the pump wiring are teed accross in a junction box with a single twin & earth cable going to the programmer
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Postby Dave From Leeds » Tue Jan 27, 2009 9:22 am

Morris,

Your latest post has given me some ideas about the possible history of your daughter's heating system configuration. Given the lack of motorised valves and thermostats I suspect that originally it was a basic gravity hot water and pumped central CH system. In such a system, although the programmer has separate slide switches for the HW and CH, it is configured so that the CH cannot be on without the HW. Some programmers achieve this by a mechanical link between the two slide switches. The Honeywell ST699/799 programmers do it by means of internal wiring (in the base plate) that allows the boiler to fire up when CH only is selected. Without motorised valves a gravity fed hot water system will come on whenever the boiler is running whether or not the HW slide is set to be on. If you look on the Screwfix website (screwfix.com) and select Plumbing then Central Heating Controls, you will find your programmer listed. In its Instruction Manual (after all the wiring diagrams) it mentions putting a “Heating and Hot Water” sticker over the word “Heating” above the CH slide switch for this very reason.

I think that what may have happened is that when the CH was on, it took the lion's share of the heat from the boiler and the water was not getting hot enough. It could be therefore that installing the hot water pump got round this problem. Again referring to the programmer’s Instruction Manual, if you look at the “Basic System 1” wiring diagram the feed for the CH pump, and therefore your HW pump based on what you said about them being wired together, comes off the CH control..

Here’s what I suggest you do now.

First of all set the slide switches to HW only (CH off). If all the garbage above is correct, the HW pump will remain stopped but the water should warm up. If so, disconnect the hot water pump at the junction box then set both slide switches to their current settings. If with this arrangement the CH works but the water doesn't heat up enough, then interrupting the existing electrical supply to that pump via a cylinder stat will almost certainly sort the matter out for you. If the water still gets as hot as it does now you'll probably also need a motorised valve in the HW pipework controlled by the cylinder stat as I suggested once before. In that case you’d need to take the live feed for the cylinder stat from terminal 8 in your programmer then split the output from the stat to both the HW pump and the valve, otherwise the motorised valve would never open when HW only was selected on the programmer, consequently no hot water. This also means that the HW pump would run on demand from the cylinder stat whether or not the CH was in use.

Finally, you may need to remove the thermostatic valve from one of the radiators since, if all the thermostatic valves were to close off at the same time, you would potentially have the CH pump working against a closed system. This is unlikely I know, but as my former employer’s safety manager used to say: “If it can happen, it will!!!”

There, I’ve covered everything I can think of in this single post. Sorry it’s so long!!
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Postby Dave From Leeds » Thu Jan 29, 2009 1:58 pm

I'm bringing this thread back to the front page in case morris has not yet read my latest (long) post, and thinks that the thread has disappeared when he has a look. The Keywords Search message from the doctor that seems to have been automatically added to a lot of threads at around 1230 hrs today has pushed a lot of live threads out of sight.
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