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Help getting my head around my central heating - only one 2 port motorised valve

Discussion in 'Plumbing and Central Heating' started by jonboy999, 28 Dec 2017.

  1. jonboy999

    jonboy999

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    Would be grateful for any help because it's driving me nuts. The problem, in brief one of hot water, but very weak radiators. I'm trying to get my head around possible causes before I possibly get the hard sell on a powerflush when I call someone round.

    System - F&E system, approx 15 years old (maybe much more) Ideal FF280 boiler.
    Boiler on ground floor, hot water cylinder (HWC) on 1st floor, F&E tank in loft.

    What I can't understand is the piping/valving setup.

    In the airing cupboard with the HWC, the hot water pump outflow splits. One leg to the inflow on the HWC, the other leg has a 2 port motorised valve, and continues to the radiators (I assume, as the pipe leaves the airing cupboard and out of view).

    There is what I assume is a hand-controlled bypass valve between the inflow and outflow on the HWC.

    There is only one motorised valve that I can see and it is the 2 port in the location described above. I've seen lots of diagrams of systems with 2 two-port motorised valves, or a single 3 port, but not a single 2-port.

    So how can the flow go to the central heating without a large portion also going through the HWC and being 'wasted', meaning not enough flow goes to the radiators? This is what I think might be happening, but as I am clearly not understanding how the whole thing works, I don't want to jump to conclusions.

    Is the system balanced by the relative resistances of the HWC circuit vs the radiator circuit, when the motorised valve is open? I can understand when the motorised valve is shut, everything goes to the HWC, but what happens when the HWC is hot enough, and full flow is needed to the rads? I could understand if the pump's outflow went to the rads only, but it's pumping to the rads and HWC together! :eek:

    All the rads are more or less equally weak. By playing around with the radiator balancing, I can make any one radiator quite hot, but only one or maybe two. Anymore rads turned on and lukewarm is the best I can hope for.

    I don't think sludging is the problem, due to the fact I can get any single rad quite hot by shutting off all the others - unless flow to the rads rather than the HWC depends on the rad circuit being clean enough to be so low resistance that flow doesn't all go the HWC (which has no motorised valve to isolate it).

    Sorry, long post but hope that explains it ok!
    Thanks
    Jon
     
    Last edited: 29 Dec 2017
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  3. jonboy999

    jonboy999

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    Just edited the post, as I kept writing boiler instead of hot water cylinder, meaning the whole post made no sense.
     
  4. Terry lambert

    Terry lambert

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    Can you post a pic
     
  5. John D v2.0

    John D v2.0

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    Sounds like your suspicion is correct, of it really as at your description.
    One question, is the hot water really hot when you've been using the heatin ? Does it heat when you turn off the hot water programmer?
     
  6. jonboy999

    jonboy999

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    Terry, I'll try and draw a diagram later, the cupboard is too cramped for a photo.

    John - yes, the hot water gets hot when only the heating is on. I left the water heating program off all day yesterday and the water was still hot.

    I'm just trying to decide if

    a) this was actually a reasonable way to have been plumbed when the system was put in, or if someone who didn't know what they were doing has bodged it sometime since then (house fairly new to me so don't know the history)

    and

    b) whether i need to get it replumbed in order to ever have decent heating.
     
  7. jonboy999

    jonboy999

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    One more thing, the outflow and inflow pipes from the boiler are both very hot, which fits in to my theory of the water bypassing through the HWC, while still leaving the radiators only lukewarm. I can't find any other bypass pipes anywhere.
     
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  8. John D v2.0

    John D v2.0

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    Your coil is basically a second bypass and usually has little resistance. You could try turning the coil down to get a nice middle ground of there's a suitable valve, but that might slow your hot water recovery times,
    the gold solution would be to add a motorised valve and adjust the wiring as necessary to open the dhw valve instead of just turning on the boiler when dhw heat demand. Then the valve could switch on the boiler once it's opened.
     
  9. John D v2.0

    John D v2.0

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    All good detective work, so sounds like it all makes sense. If you do add another valve, assuming a modern boiler if it doesn't have a built in bypass you'd need to add one somewhere before the valves.
    It's possible your system used to be a gravity system not fully pumped and hasn't been converted properly.
    Or maybe still is and the pump is in the wrong place!
     
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  11. jonboy999

    jonboy999

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    Thanks John. From your first post I'm assuming you mean the coil in the HWC? There is no valve or way to restrict flow to that in the current piping. There appears to be a bypass with a valve outside the HWC, between the inflow and outflow to the HWC, but I think shutting that would still just send all the flow through the HWC coil, and as you say that has little resistance.

    I wonder if you're right about the pump being in the wrong place - if the pump was located after the takeoff to the HWC, I think that would make it work correctly? Though I know from past experience that flow in piping isn't always intuitive, for me anyway!
    Your gold solution about adding a 2nd motorised valve (with suitabaly located bypass) seems like the best solution though. I'll ask about that when I get a plumber to visit, but really useful to have an idea about it beforehand.
     
  12. John D v2.0

    John D v2.0

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    For a low water content ie modern boiler you'd need to be fully pumped so you couldn't just move the pump (back to where it was before the last boiler change?).
    So the problem could well be a half assed conversion job from gravity to fully pumped when a new boiler was fitted.
    If it worked reasonably maybe it was worth a cheap job.
    No idea why there's a coil in the hot water cylinder and a bypass across it though.
     
  13. jonboy999

    jonboy999

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    Right ok, so making the Hot water side of things gravity fed while the radiator circuit was pump fed wouldn't be a good idea for a modern boiler? Got you, so definitely makes sense if replumbing it to put in a second motorised valve before the HWC, rather than move the pump.
     
  14. John D v2.0

    John D v2.0

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    Spot on, modern boiler doesn't have enough water in I to do gravity HW.
    Second valve, and associated wiring, make sure you still have a bypass and pump overrun and you'll be fine.
    Hopefully the problem hasn't been exacerbated by sludge or anything in your rads. That's my only concern with there being no recent changes to the system
     
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  15. jonboy999

    jonboy999

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    Thanks. I suspect the issue has worsened slowly over time by sludge build up and increasing the resistance of the rad circuit. However my mother (it's my parent's house, they're getting on a bit and somewhat vague) say it was all flushed out due to cool rads, a couple of years ago without helping much. So even if still sludge there, then i think getting the pipework sorted first, then try reflsuhing if still not perfect afterwards is the way to go.
     
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  16. jonboy999

    jonboy999

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    Alright, got a picture, would welcome a second opinion on if I'm giong crazy or not. I took a photo of the backside of the pump and there is an arrow pointing down, so I have assumed that is the direction of water flow.
    I mentioned earlier about a bypass between the inflow and outflow on the HWC coil. Actually this bypasses the radiator circuit, but due to where they branch off before the motorized valve, and go to the HWC outflow, both the HWC coil both the HWC coil and the bypass effectively act as bypasses to the radiator circuit...



    Also there is a boiler optimizer device in the shot (energy minder auto), which is supposed to have temp sensors on the inflow and outlfow of the HWC coil, that appear to be on completely the wrong pipes. Not sure if the kids have been playing around with those.


    pipework labelled.png

    pipework2.jpg
     
  17. John D v2.0

    John D v2.0

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    With that dangerous wiring you need to get it sorted ASAP with kids! :eek: No cover on the enclosure, cable without strain relief not clipped, so if they pull it they could have exposed live wires flapping around!

    Regarding the pipework it seems it is as we said before(y)
     
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