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Can i add an extra pump to central heating to improve flow?

Postby austen » Tue Feb 10, 2009 10:02 am

My house is very long, and the rear part added since the boiler and central heating sytem. The front part seems to have a proper 22mm copper piped in sytem with 15mm spurs going off to the rads. These all work fine and get nice and hot, but the rear part of the house (upstairs and downstairs has been added onto this system as another "ring" with spurs going off to the rads. These rads do not get that hot, and since taking two of them off to decorate the are stone cold. Its hard to explain how its been done, jut imagine a spur being taken off the main system, with sub spurs off that to each radiator. I have been told by an engineer that the pump isn't big enough for the 10 rads and size of house, so suggested upgrading the pump. But i'm not convinced this will help the rear part of the house. I have a spare pump (about the same flow rate) and was thinking of adding it into the rear house system spur to boost the flow around this part. Do you think this would work????
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Postby htg engineer » Tue Feb 10, 2009 11:41 am

It will as long as both pumps are on the flow or both on the return - you don't want them pumping against each other.

If your existing pumps is old - upgrading the pump may work. this will be less work as, where will you fit the second pump ? how will you wire it ?


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Postby austen » Tue Feb 10, 2009 11:48 am

[quote="htg engineer"]It will as long as both pumps are on the flow or both on the return - you don't want them pumping against each other.

If your existing pumps is old - upgrading the pump may work. this will be less work as, where will you fit the second pump ? how will you wire it ?


htg[/quote]

No problem in getting the flow in the correct direction. The boiler is in the cellar and the pipe work where it all splits is next to the boiler and easily accessible. I'll also just wire the extra pump in from the feed to existing pump so will switch on and off at the same time.

Maybe the pump is on the way out, but is suppose i have nothing to loose as the spare pump i have is free.

I rekon i have an air lock somewhere in the extension aswell, but plan is to drain system, put extra pump in and then refill, fingers crosssed the sir lock disappears.
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Postby austen » Tue Feb 10, 2009 12:19 pm

this is the design, which with my very limited knowledge looks rubbish, and i assume the water is virtually bypassing the 15mm section as the easier route is the 22mm. Why on earth the stop valves were put where they are is beyond me, if they were the other side of the joint then you could close off the 22mm section and pump it round the 15mm section on its own, or at leats restrict the flow of the 22mm section forcing it round the 15mm!.
I have marked up where i was thinking of adding the pump.

[IMG]http://img.photobucket.com/albums/v36/agreenway/crapheating.jpg[/IMG]
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Postby htg engineer » Tue Feb 10, 2009 5:55 pm

You don't really want the two pumps in close proximity of each other, for example say you have 5 radiators that don't work, install the pump before those but after the ones that are working for best performance.

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Postby rosebery » Wed Feb 11, 2009 1:00 am

Are you sure you don't have an airlock?

I'd also suggest balancing the system before trying anything else more expensive.
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Postby pvbarri » Mon Jan 11, 2021 3:02 pm

I came across the subject forum while doing a Google search for an issue I have had at home. Without going into a long story, I would like to find out the likely result of having 2 pumps (1 in a gas boiler and one other) working a g a i n s t each other in a domestic sealed heating/water system with 3 heating zones (2 under-floor and 1 radiators), 1 hot-water zone, 3 motorised valves and numerous pipe joints)? If nobody can help me, I would greatly appreciate any steerage/advice on where such an assessment or relevant information might be found. Many thanks in advance.
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Postby ericmark » Tue Jan 12, 2021 2:53 pm

I have two pumps, it is a real pain, it means two relays, two thermostats, etc. I wish only one pump.

So my house 12 rooms not counting hall and toilet etc, 4 rooms on one pump and 8 on the other, as it is one pump switched off as simply don't use the 4 rooms in the flat under the house, but I also had to fit a motorised valves, as with one pump only running the radiators still worked but flow reversed.

I use electronic TRV heads, set so when central heating starts up, some rooms are heated before others, so for example returning home at 6 pm, so kitchen is first room to be used so that starts heating 5 pm, dinning room next so that starts at 5:15 pm, then living room at 5:30 pm, and bedroom at 10 pm.

It depends on boiler, does it modulate etc. The biggest problem with central heating is when a wall thermostat turns off the boiler prematurely, as each room reaches the target temperature the TRV closes and so other rooms have more flow.
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Postby pvbarri » Thu Jan 14, 2021 9:45 am

Hi Eric, (or is it Mark?) Many thanks for your reply - it all helps with the knowledge base - but (and my apologies for not giving a more complete background to the question) I was really going for an un-guided response - if that makes any sense. So, here's the actual problem and specific questions.
Background: The gas boiler in my home was replaced around 3 years ago but with the flow and return pipes fitted the wrong way round. The system has an additional pump (designed to work in series with the boiler pump) for a better water flow through the hot water tank. Because the flow and return pipes were the wrong way round the boiler and additional pumps were actually working against each other.
What I would really like to know is; what impact, on a closed heating/water system, there might be from having 2 pumps working against each other over a 3-year period? And, even more specifically, if the increased 'pressure' on the system caused by this could cause a pipe joint to fail?
Paul.
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Postby ericmark » Sat Jan 16, 2021 11:17 am

Sorry I am an electrician, although I did work for SLD pumps so understand pumping to some extent, but with central heating we have a by-pass valve, the standard idea is as each TRV head closes the by-pass opens and hot water is returned to boiler and the boiler reduces output, this can include a variable output pump, so working out what would happen in your system would be complex.

If trying to get compensation then it's all down to the letters behind the name of inspector, does not really matter how good he is, he needs to show a court how good he is, so electrical wise the C&G 2391 shows the guy can inspect and test, which was not taught on my degree, but my degree is level 5 and the C&G 2391 is level 3 so courts tend to take my word over some one with C&G 2391 even when really he is better qualified.

Collage lecturer likely the best you can get. Forum is useless as you have no idea in most cases how qualified the person is, my daughter-in-law seems to collect trades, qualified as plumber, lock smith, bus driver, and cook, but only really good as a cook, well never rode on her bus, but did go on her narrow boat, seems that's a contact sport the way she pilots it!
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Postby pvbarri » Sat Jan 16, 2021 11:35 am

Many thanks for that. I'm getting a sense that, particularly for the clueless (e.g. me), it's going to be very difficult to get a precise answer. It isn't so much about compensation it's about the technical competency of a firm and their response to questions. They simply should not be able to get away with that low level of competency or poor customer relations. Anyway, many thanks for your help. In the, albeit unlikely, event of making headway I'll update the forum.
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Postby ericmark » Sun Jan 17, 2021 4:48 pm

Your not on your own, this house on three floors is rather large for an 18/24 oil fired boiler, but it is ample the way now configured.

The original however was a mess, two pumps and thermo syphon clearly the installed thought one pump for flat under main house and one pump for main house.

However the control was simply not there, had to manually plug in the pump.

Also one pump would cause reverse flow through the other, so simply switch one off when that part of house not being used did not work.

At nearly 70 I would have a problem working in the confined space to fit motorised valves, I expected one pump and two motorised valves, but for some reason I have two pumps.

The normal way is thermostat works the motorised valve, and the motorised valve works boiler and pump, but could not connect boiler and pumps all to same supply so means also need relays.

I wanted a bypass valve, but pumps are on the return, so that will not work. What seems really daft is the installer has actually put his name on the boiler for serving etc. If I had installed such a poor system last thing I would want to do is put my name on it, at least I know who not to use.

But a central heating pump is good for around 15 psi, so two 30 psi and pipes are used on mains pressure which is well over 30 psi (2 bar) so can take the pressure, but normal by-pass valve adjustment range : 0.1 to 0.5 bar. So I would think the high pressure would cause either the by-pass valve to lift or cause a problem with the thermostatic radiator valves (TRV).

In the old days the TRV was directional, today most work either way, but better on inlet as then closer to hot part of radiator and where duel sensors used one for air and one for water, the compensation for water temperature works better on the feed side.

On my system using electronic TRV heads transformed the system, rooms only heated when required.
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