Underfloor heating question

Discussion in 'Plumbing and Central Heating' started by Doobrey, 14 Mar 2012.

  1. Doobrey

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    Guys,

    I am trying to get to the bottom of why my underfloor heating isnt quite working correctly.

    Firstly, I have two manifolds.


    The Bottom manifold is where the hot water comes into the system. The water then flows to the output valves. These are open or closed. Currently all open.

    The Top manifold is the return. Each "Zone" has an adjustment valve, which can be opened up or closed, depending upon how many turns, will allow more or less water to return through the system.

    First question. Is this right? Shouldn't the adjustable valve be on the bottom?

    Secondly, I "think" I have heard that the water from the boiler should be set to 65 degrees. Now, is this the water temperature on the side of the cylinder in the airing cupboard (Photo below).


    Or do I set this physically on the boiler? (Photo below)


    Thirdly, I have heard about balancing the system. My understanding of this is that each zone has a different length of pipe. If the pipe length is short, then you need to send less hot water there, as the return water will be back into the system quicker.

    I have also read somewhere about if the boiler turns off and on when its trying to send hot water to the UFH. Apparently if I turn off all of the UFH (Close all valves) and let it cool down, then open just one zone, the boiler should fire up and service that zone until it reaches the desired temperature. I "think" my boiler turns off and on regularly, rather than staying on. I am going to try this out later today to confirm. My question is, if the boiler is turning off/on rapidly, what could be the cause? Faulty pump, balancing, faulty valve, something else?


    Can anyone guide me please.

    Doobs.
     
  2. stem

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    Might be able to help with some items for you. The cylinder thermostat is to control the temperature of the stored hot water supply to the kitchen / bathroom taps. It's nothing to do with the underfloor heating.

    The boiler thermostat is where you set the temperature of the hot water leaving the boiler. However, there likely will also be a thermostatic mixing valve near the pump / manifold that controls the temperature of the water in the underfloor section. Underfloor heating does operates at lower temperatures than radiators, as it has a larger surface to emit the heat from and I guess so that you don't burn your feet.

    Condensing boilers are generally stated as operating more efficiently with low return temperatures, but yours looks like an old non condensing Baxi Solo. The Solo has a thermostat that maintains the water leaving the boiler at the temperature set by the small knob, so it turns the gas on and off as required. If it kept running permanently the water would boil. The switching on and off you describe sounds perfectly normal.

    With traditional radiators the valve on the return pipe is often used to balance the system. Personally I don't see why an underfloor system should be any different, but I'm not a UFH expert.

    You are right about the lengths of the tubes and the balancing. The valves distribute the water flow by imposing a variable resistance to the flow of water around each loop so that the water is distributed evenly, instead of just taking the easy route around the shortest loop.

    You don't say what's wrong with your heating, perhaps more details would allow further assistance.
     
  3. Doobrey

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    Hi Stem,

    Thank you for coming back to me.

    What is wrong is that the living room simply doesnt get warm enough. I have been working with the company that makes the products used in the UFH to try and determine where the problem might lie.

    We have identified a faulty lockshield valve, which obviously wont help with the balancing! so I am ordering one of those, but the weirdest thing is that the water that comes past the mixing valve into the UFH pump then reaches the manifold via copper pipes, arrives under my stairs at 38 degrees, then flows down a small copper pipe (lets call it 2 ft) and turns horizontal. After this turn, the temperature is 10 degrees lower! so enters the manifold around 25 degrees. (Something doesn't seem right here). When I measure the temperature of the water once it has passed the manifold and has just gone past the lockshield valve, it sits around 35 degrees when the boiler is not on, then rises to 45 degrees when it is pumping.

    I am no expert, but does the difference in heat on the copper pipes, after the pump, sound right? Perhaps air in the system?

    Doobs.
     
  4. DeltaT2

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    Sounds as if it's purely down to poor circulation on the UFH loops mate. That could be as a result of air or a blockage in a loop.

    If? it's been sized correctly the circulation pump is sized for the index loop, but if a loop is blocked the pump doesn't care, it'll still work away quite happily.
     
  5. Doobrey

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    Ok guys....

    I think I have almost solved this.

    The main 83m loop appears to have reduced flow in the pipe. The reason I know this is that I have attached a cold water feed to the flow manifold and set up each loop as instructed.

    The second biggest loop 50+ meters, went cold from the flow instantly (as expected) and within say 10 seconds, the return was equally as cold. Now the biggest loop 83+ meters, the water contained with the pipes on the flow side were cold instantly, but the return, even after 5 -6 minutes, was still not cold, indicating the warm water still resides. In my mind, that means a reduced flow of water, hence a blockage in the pipe.

    So....Any suggestions on how to clear the pipe? I have tried reversing the flow of water - helped a little, but it is definately reduced flow.

    Any help would be much appreciated.

    Doobs.
     
  6. Dan_Robinson

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    Unless your mains pressure is pathetic, I doubt a blockage like that is shift-able if mains water doesn't do it.

    You could try air pressure up to the rating of the pipe, but chances are the pipe is kinked in the floor.
     
  7. middlesbrough

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    Looking for an opertunity to used your heat imaging gun ? ;)
     
  8. Doobrey

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    Hmm, not sure on the kinking as it is embedded in scree... And has worked previously. I have flushed though the system but it seems like something is blocking it... Is a power flush worth looking into?
     
  9. Dan_Robinson

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    :LOL: :LOL: Norfolk might be a bit of a trek.

    As for powerflushing.... what state was the system water in?
     
  10. Norcon

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    Are you sure the appropiate valves on the manifold are open?

    Try disconnecting the loop from the manifold and connect the mains flow directly to the pipe.
     
  11. Doobrey

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    The water was initially black coming out, then it cleared.

    I am pretty sure it's the right valve as i had to open it :)

    How can I connect a hose directly to the valve ? Remembering that it is connected to the manifold. I would have to unconnected it with a spanner, but then not sure how I would connect a hose to it???

    Doobs.
     
  12. middlesbrough

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    If your not sure how to connect a hose to a pipe then maybe youd be better off calling a plumber out :idea:
     
  13. Doobrey

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    LOL!

    No - what I mean is if I remove the lockshield valve (assuming this is what you are saying)... removing the lockshield valve from the manifold - yes I can do this - but how to connect into the 22mm thread from a hose pipe?!?
     
  14. Agile

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    you dont make it clear if its a new problem or always been like that.

    Cylinderstat should be at 55-60 and boiler 60-65 C

    83m seems a rather long loop and would require careful balancing wheb used with much shorter loops.

    To help understand whats going on a flow and return temp messurement is needed on each loop.

    Why not call one of your local UFH experts?

    Tony
     
  15. Norcon

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    Which valve did you open?
    Bottom manifold or top manifold? And which loop from looking at your image above?
     

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