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central heating only comes on with h water, stumped engineer

Discussion in 'Plumbing and Central Heating' started by bonkersbill, 17 Oct 2011.

  1. Mikefromlondon

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    Thanks Matt, I can see the point now, since if the pump was connected to the return tapping , it would force the water in correctly through the boiler's heat exchanger. All depending of course how the pump is connected and in which direction it is flowing, but yes, good point and thanks again. cheers.
     
  2. doitall

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    What I asked for is not an option, I/we need to know, and until we get answer we are wasting out time.

    For your information only the pump is sucking the water from the boiler, port AB will get hot first with the pump running, even when it's connected wrong.
     
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  3. UpgradeME

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  4. bonkersbill

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    Thanks Doitall, at last an explanation i understand as to why testing with the pump on does not work, this could have saved me alot of time had i understood this earlier.
    Heres my solution to figure out which 28mm pipe is which, i will close off all rads, water tanks and valves, drain the system from a downstairs rad that has a drain plug lower than the boiler, remove the cylinder pipe at 3pv port B because its easy to get to, remove the top 28mm pipe conected to the boiler, i will then either blow, shout or pour water down this pipe with my missis on the other end, if any of these comes out of the 28mm pipe, its connected wrongly, if they come out of the boiler then its piped correctly, can anyone see any flaws or reasons not to do this?
     
  5. doitall

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    :rolleyes: The sooner you, stop thinking and leaving it to the pros the better your chances are :rolleyes:

    Your plan is flawed because we don't know what else is connected wrong.

    Put the two pics together in a drawing, and ID the capped pipe
     
  6. bonkersbill

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    i've already put the 2 pics on my last drawing showing the capped off pipe. At the moment i have the gas fire out, if im going to do any tests i need to do them now because i need to put it back for my heating and hot water.
     
  7. doitall

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    If your last drawing was accurate the system would work.

    You need to do the tests we asked for, with the pump off electrically.

    or trace the pipes.

    Test with the MV in all 3 positions, and the boiler on low.
     
  8. bonkersbill

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    ive done all the tests with the pump off and ive traced the pipes to the best that can be done by eye other than under the boiler, i have had 2 carpets up and been through 2 access holes to be blocked off by brick walls. if ive missed some new tests somewhere then what are they?
     
  9. matt1e

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    Looking through He has already done this
    But then again that seems to contradict this
     
  10. bonkersbill

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    Yes i believe i pointed this out that i had both pipes get hot in different tests. this is why i proposed disconecting the pipes to find out which was which.
    i was told after these tests i needed to find out what was happening at the boiler, this i have now done, so what now?
     
  11. doitall

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    Mark the pipes where they are outside of the boiler going up the wall, so you know exactly which is the flow and return.

    There is also an issue with the heating return getting hot from memory.

    You can disable the pump from the wiring center if it's difficult to get at the pump.

    Then do the tests again and post the 3 results.

    HWS only, which pipe gets hot.

    Mid position which pipe gets hot.

    Heating only which pipe gets hot.
     
  12. matt1e

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    Bill the two tests quoted should yield the same results
    it is hard to make out from the photo, is the 3port B connection going to the bottom or top cylinder connection?

    Matt
     
  13. bonkersbill

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    Port B goes to the top pipe in cyl.
    The return pipe we thought was getting hot was the 15mm which teed off to 22mm towards the boiler, this is capped off. i can only make a reasonable guess as to which of the 28mm pipes is which when it goes through 8 inch of chimney, even so, from this point up to the pump/cyl i cant tell which is which, hence my suggested test or any other, the heat test with pump disconnected definatly showed both pipes getting hot in different tests. My suggestion of disconecting the port B and top of the boiler to find out if these are both the same pipe could resolve this baring any hidden tees which we cant varify anyway.
     
  14. stardanny

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    The pipe at top is 28mm flow.
    The pipe at the back top is the 22mm flow that is capped when it changed to fully pumped.
    The bottom one is the injector tee with 28mm return at bottom of tee and 22mm heating return at side of tee.

    There could be trace of where the old heating pump used to be with a piece of pipe in place of pump. Could be in box in or under ground floor.

    This is fine. Correctly piped.

    The best way is to trace / look both 28mm pipes from boiler tappings to cylinder tapping/pump inlet. Take your time and work out. Any good pipe fitter like me can work out which it which.

    Dan.
     
  15. Agile

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    I like that idea !

    Make sure she wears a thin white tee shirt so that you can easily see if she has got wet.
     
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