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Pump in wrong place on Open Vent system...

Discussion in 'Plumbing and Central Heating' started by littlepigeon, 15 Sep 2018.

  1. littlepigeon

    littlepigeon

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    Hi all,

    After a bit if advice if poss.

    I have an old open vent system in my house, and from a fair old bit of investigation I definitely think the pump is in the wrong place. It's straight after the boiler on the flow side, before the open vent. From my workings it looks like it should be after the vent. However, my boiler is on the ground floor and the vent right up in the loft a fair old distance away. I've also noted that it seems the pump should be wired into the boiler for switching and power. This means to get the nesaserry configuration I think all new wiring would need running all the way from the boiler to the loft. This would mean a lot of destruction and redecorating. Unless by chance there is some where I could wire the pump to in the loft, however I'm not sure what is what with regards to wiring up there, there is a control box and the two valves and a fair bit of wiring.

    Anyway, I was wondering if it's going to be a big pain to move the pump to the loft, what about just moving the pump to be on the boiler return pipe rather than the flow, could this be a better option.

    The problems I'm seeing with the system is air in system, and just recently I've noticed I'm getting hot water pushed back into the feed/expansion tank. I can hear a glug every now and again, and the header tank water is a little warm if I dip my finger in.

    Many thanks all
     
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  3. ReganAndCarter

    ReganAndCarter

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    It does sound wrong, maybe some photos would help. The diagram on this link shows the usual feed and vent pipe arrangements, i.e. pipes before the pump. Sounds like yours are after the pump.

    http://www.home-heating-systems-and-solutions.com/diy-heating-plumbing-tips-6.html

    Putting the pump on return before boiler wouldn't help as you would still be pumping towards the feed and vent pipes, not away from them.

    As for wiring, most newer boilers have the pump wired into the boiler, because the boiler's heat exchanger needs a throughput of water after the boiler stops firing to cool the exchanger. This is called pump overrun. Without this period of pump circulating after boiler finishes firing, modern boilers can be damaged. Many older boilers with cast iron heat exchangers don't need overrun and the pump is wired directly into the heating wiring centre. The boiler and pump will stop at the same time. So, you can see it very much depends on the boiler as to how it should be configured.
     
  4. littlepigeon

    littlepigeon

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    Yeah.. .I thought that would be the case, and I bet that's why whoever installed the newer boiler into the old system has put the pump where they have.... Lazy cop out! :(
     
  5. littlepigeon

    littlepigeon

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    I have just had a hive setup introduced into my system, so I wonder if that has made any of the existing wiring running from the boiler to loft redundant, which could then be repurposed as a run to connect pump to boiler from loft, if I had the pump moved?Worth looking into I guess?
     
  6. littlepigeon

    littlepigeon

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    Ok .. just doing some more investigation, and the header tank heating up seems more prevalent when just the water cyl/tank is being heated and central heating valve is off. I think I may have worked out why, or what will probably be making the matter worse. It looks like the route for the heating water from the main 22mm feed and return pipe going to and from the boiler is just a 15mm pipe with the water cyl control valve on. However the exit from the hot water tank coil is still 22mm. Surely this will restrict the water flow into the cylinder heat coil, meaning it will take a lesser path of resistance which is up the feed pipe into the tank. Which i presume is why every now and again i get a glug which is the warm water from the boiler making its way into the header tank.

    I cant really get any decent pictures, so will try and draw a diagram of whats going on to help.

    Cheers all.
     
  7. littlepigeon

    littlepigeon

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    Ok .. dodgy drawing i know... but hopefully this gives you an idea of whats going on. The pipe thicknesses are to show 22mm vs 15mm. I would think that 15mm pipe is restricting the flow when the CH valve is closed so the water is finding its way up the cold feed pipe. Or would that not be an issue?

    here are also a load of red turning isolating valves in places. There is one on that weird small bypass pipe, and one on the 22mm pipe coming out of the bottom of the cyl. I have read they could be for balancing the system. They are all wide open though now, as the boiler is firing restricted flow errors when just the hot water is on. I think ideally that pump should bejust after that cold feed pipe from the F&E tank, but getting wiring from the boiler to there is going to be a right old nightmare from what i can see, unless i could run a cable externally maybe (is that a possibility, or against some sort of regs?)

    Any suggestions would be great. I've had a few people round for various things over the years and they always seem to shy away from this kind of system and want to sell me a new boiler etc... I think this just needs setting up right.

    many thanks.

    CH diagram.jpg
     
  8. picasso

    picasso

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    There should be an arrow on the body of the pump, which way is it pointing? its normal for the water in the f and e expansion tank to get warm.
     
  9. littlepigeon

    littlepigeon

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    I can't see an arrow unless its up on top. Its quite high, so cant see the top easily. However, the pump is pumping away from the boiler and towards the vent.
     
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  11. fixitflav

    fixitflav

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    Why the loft? The boiler and pump may not be close together, as you'd prefer, but neither, or any other electrical kit, is likely to be in the loft.
     
  12. littlepigeon

    littlepigeon

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    Because the water tank, expansion tanks, valves etc are all up there. For the pump to be placed where i think it should be (after the feed but before the valves), it would need to be there (i think).
     
  13. gasmanstu72

    gasmanstu72

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    CH diagram.jpg

    this is where your pump needs to be, if there's no room on that pipe you're going to have to re-configure the pipework to accommodate it
     
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  14. fixitflav

    fixitflav

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    OK, but I don't think it's a good idea to put the pump in the loft, even if it's piped boiler - open vent - cold feed - pump as recommended in the link in #2. The pressure at pump suction should preferably be as high as possible to avoid cavitation. Cold feed close to pump suction is best, as that is a constant pressure, everywhere else is at higher pressure (relative to same level datum) (I may not have explained that too well, but I think you'll get what I mean).
    I'm not sure I understand your layout sketch. Can you do one showing the boiler as well? preferably with the various bits of kit grouped to give some idea of locations and levels.
     
  15. picasso

    picasso

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    If your drawing was accurate the vent would be running continually every time the pump ran, have another look and see if you have the pipe layout accurate.
     
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  16. littlepigeon

    littlepigeon

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    Basically, all that stuff on the left of the picture is up in the loft, the boiler is on the ground floor at the back of the house with the pump right after it on the flow pipe. I have attached a picture but the pipe labelled return is incorrect. I think that's actually the hit water going to the taps etc.... The pipe that's actually returning to the boiler is the white plastic one you can see that comes out the bottom of the cyl
    Screenshot_20180917-001823_Dropbox.jpg
     
    Last edited: 17 Sep 2018
  17. littlepigeon

    littlepigeon

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    I can't see that anything is coming out the vent when I've monitored it for a while, but I presume it's because it's quite high so it finds its way round the junction to the cold feed before actually making it to the end of the vent. It does get quite warm so I presume some hot water is making it up the vent, but just not far enough to come out the end of it. However it is making it up the cold feed as you hear it glug every now and again when only heating water not CH. So I guess that's either hot water or air. Given the f and e water warms up I presume its actually warm water making it up there.
     
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