Underfloor heating retrofit not heating up

Discussion in 'Plumbers' Talk' started by tpowell_12, Nov 11, 2017.

  1. tpowell_12

    tpowell_12 New Member

    My plumber has installed underfloor heating in my home connecting it to my existing heating and hot water system.

    We have a system boiler on the ground floor with the boiler pump for the existing heating and hot water located in the airing cupboard on the first floor.

    My plumber has teed off the flow directly above the boiler ie. between the boiler and the boiler pump is this normal, should this work?

    It seems to me (I am not a plumber so may well be talking ****!) that teeing off before the pump means there is now negative/no flow (not pressure) in that section of pipework. I have included 2 images to illustrate the different approaches.

    My existing heating and hot water still work fine but something isnt working in the underfloor heating and it seems to not be circulating warm water. The underfloor heating system has been dismantled with no obvious errors.

    Attached Files:

  2. koolpc

    koolpc Well-Known Member

    Call plumber back to sort out....
  3. tpowell_12

    tpowell_12 New Member

    Thanks for the reply, not sure it has helped in answering the question...

    For context; I've had several plumbers look at it but none seem to be able to diagnose the problem, hence why I have posted my question here.
  4. leesparkykent

    leesparkykent Well-Known Member

    What boiler do you have? If it's a system boiler you wouldn't usually have an external pump.
  5. tpowell_12

    tpowell_12 New Member

    Glow worm hxi30
  6. leesparkykent

    leesparkykent Well-Known Member

    Yes the UFH valve should be after the pump not before. The boiler is a heat only boiler not system.
  7. tpowell_12

    tpowell_12 New Member

    Brilliant, thank you for confirmation.

    To save cutting up anymore floors/walls above, would it be ok to add a second boiler pump before the ufh tee off? Would this increase pressure too much?
  8. koolpc

    koolpc Well-Known Member

    Didn't the plumber test it all when he installed it?
  9. tpowell_12

    tpowell_12 New Member

    He was unable to fully test it as the electrics hadn't been installed at the time.
    Since the electrics have been installed we have had 2 plumbers look at the connecting pipework plus a third one who initailly installed the underfloor heating loop came to check over his part which seems to be working as expected.
    All pipework looks good and correct. As I said my concern is that the connection to the flow is in the wrong place.
    Do you know if it is ok to add a second pump to a heating/hot water system? Will this cause incorrect pressure elsewhere or is it safe to add another pump?
  10. Jeepers.

    Let's get this right - you've had an original plumber who installed the UFH system, and a different one out to connect the pipework to this?


    And this second plumber seemingly connected the 'flow' to the UFH system before the pump - where there isn't any flow.

    Which you - as a professed layman, with no plumbing experience - have sussed out for yourself is weird?

    But which two subsequent 'plumbers' have not been able to arrive at that same conclusion?

    Even when you - presumably - did point this out to them?

    I don't know where to start - too many questions here...

    Like (1) why didn't you call out the 'second' plumber when the system clearly didn't work? (2) why did you use a second plumber anyways? (3) what's wrong with the third plumber when he didn't work out what you have done? (4) What's wrong with your 4th plumber when...

    To answer your question, there is no reason - in theory - why you couldn't add a further pump to most systems if it's needed. But what should it be needed here? Why not move a pipe...?

    If, for some insane reason, you really are planning to fit a pump where you say, how will it be controlled? How will it only come on with the UFH system? How will you prevent it from pulling against the other pump if that one is also on?

    Are you NUTS man?

    Why not move one pipe to the 'correct' position? And why have three plumbers not worked this out?

    Something weird going on...
  11. tpowell_12

    tpowell_12 New Member

    Haha, thanks for the reply! lots of queries, and I think you have answered my question , which to summarise is that it's fine to connect a second pump so long as the electrics work it correctly, however this would be a strange solution!?

    Installation of pump 2 would be after the boiler but before the ufh tee off (this prevents it pulling against existing pump).
    New pump would be wired into boiler to always be on when boiler is on. Ufh stat talks directly to boiler thus operating new pump simultaneously. Existing heating and hot water electrics can then remain untouched.

    The reason to (potentially) not move the pipe itself is this would involve cutting up the floor/ceiling through half the house to plumb it to its rightful location (in the airing cupbard after the existing pump)

    To answer your other questions...
    Plumber 1 (installer of ufh) only installs ufh ie. installs the manifold, lays the pipework and does the screeding of the floor.

    Plumber 3 is a 'more experienced' contact of plumber 2 who is a friend and was doing me a favour connecting up house to ufh.

    There was an electrical issue at the same time which was confusing the situation, plumber 2&3 suspected an air lock, and yes, I a 'layman' suggested this might be the issue to which all 3 were sceptical!

    Anyway, thanks for all your help everyone that replied, we now can be reasonably sure of the problem and have a couple of potential solutions.
  12. Pollowick

    Pollowick Well-Known Member

    As you will be adding a pump before the branch, is there actually a requirement for the original pump to remain in the system?

    I would suggest it can come out and a straight feed through connected there. Others may wish to comment.

    I have UFH where a single pump pushed the water round the main heating, hot water and to the thermo-mixer for the UFH and at that point the UFH pump takes over pumping round that system as it appears your is doing.
    Deleted member 33931 likes this.
  13. tpowell_12

    tpowell_12 New Member

    Great point, potentially I could move the existing pump to the new location.

    Thanks for another option!
  14. Pollowick

    Pollowick Well-Known Member

    Hopefully some of the others may also comment as to whether it is viable - I think it should be.
  15. D'oh!

    Assuming the issue is as simple as the flow take-off being before the pump, then moving the pump to before this tee is a cracking solution!

    But... why didn't at least two plumbers seemingly not realise what this issue actually is?
  16. Pollowick

    Pollowick Well-Known Member

    I thought of it just after the original post, then thought, if it is that simple, why did visiting plumbers not suggest it and wondered if there was another reason. I cannot think of one, except maybe location or the expansion pipe ...

    The UFH normally requires a pumped supply to it, and the mixer valve takes what is required and uses its own pump to circulate round the pipework and push some cool water back into the main return. I wonder if the various plumbers thought that the UFH pump was there to do everything?
  17. dcox

    dcox Member


    In your diagram, under the pump on the UFH circuit you seem to show a blending valve mixing the flow and return. Is that right? Where is the return from the UFH circuit back to the boiler?
  18. Pollowick

    Pollowick Well-Known Member

    You probably have to give the OP some leeway with te diagram - the thermostatic blending valve is a 4-port device with incoming flow and return, often actually adjacent, a UFH flow and UFH return. All four connection are shown, but the first two are on one side of the diagram. The OP has used the blue to indicate return from UFH to boiler.
  19. dcox

    dcox Member

    I think I'd temporarily link the flow and return on the boiler side just before the blending valve and check that the loop heats up - then I'd know the problem was beyond that point somewhere in the UFH circuit. It would confirm that the issue is the position of the flow take off. Can't quite understand how the four port valve works - ie what it's blending. I'll do some research for my own satisfaction.
  20. Pollowick

    Pollowick Well-Known Member

    Here is a picture of one I have installed.


    The Hot supply arrives at anywhere from 65° to 80° which it too hot for a UFH, they run down at 40° to 45° or thereabouts. The hot input has the red isolation valve. Assuming that the UFH is cold, then the valve allows a large amount of hot in whilst pushing cold water out into the return - with the blue isolator. The incoming hot is mixed with some of the existing cool water at an appropriate ratio to bring the UFH circulation up to the chosen level - the white knob sets that. The valve output, in this case goes direct to the pump and from there into the feed side of the manifold. The return side of the manifold, just visible at the bottom brings in the used water which will be below the required temperature - some is returned to the main system and some mixed with the incoming hot.

    Does that make sense?

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