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isolating CH side from combi to identify pressure loss

Discussion in 'Plumbing and Central Heating' started by silver50, 25 Nov 2018.

  1. silver50

    silver50

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    Hi folks

    (Combi is a 17/18 year old Vokera Linea+)

    I posted before about this and I admit I should've got on with investigating it better but I've been nursing the boiler along topping it up. It's losing a bit more again now, I'd say it'd drop 1 bar in about 4 days. It'd drop from 1.5-2 bar to zero in under a week. I ideally want to move the boiler before long which has to be done along with other alterations. So I ideally don't want to replace it now and I certainly don't want to if my leak is on CH side. Theres a flat below mine but no obvious signs of a leak anywhere.

    History to this is

    1. A few years ago an engineer claimed to see there was pin hole leak at main heat exchanger
    2. A year or so ago another engineer serviced the boiler and thought heat exchanger seemed fine
    3. At the same time (year or so) the engineer replaced the PRV and checked expansion vessel
    (my pressure gauge isn't ever going up). I think we put stop leak into the system. It was miles better for a while.

    I've a feeling there maybe is an underfloor leak somewhere but would like to be sure hence (as I think was suggested here) isolating the heating system side for a few days.

    See pic. I'm posting because an engineer I spoke to yesterday didn't seem sure whether it was necessary to loop to flow and return together or whether you can just shut off valves. I bought two 22mm isolating valves* on the assumption they could maybe just be fitted into the flow/return pipes. I had someone here to look at it on Thursday who seemed to think it was the expansion vessel but he came without a pump then didn't return on Friday.
    (*I believe not a good idea to touch the old valves as per pic)

    Probably then get someone new this week, but I'd quite like to be able to say what I'd like done to isolate the heating. What would be best? Thanks
     

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  3. ianmcd

    ianmcd

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    your boiler is fitted with isolating valves shown in your pic but be aware that if you use these to isolate the boiler there is a good chance that they will leak when you open them back up again, the engineer that told you that the heat exchanger was leaking could very well be correct, as it involves removing the combustion cover I am not allowed by site rules to advise you how to check but it is very common for these heat exchangers to leak at the rear left hand side weld
     
  4. silver50

    silver50

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    Thanks Ian, I must say the one thing I'm wondering about is the heat exchanger but I've been told if they go they'll leak really badly. Is there likely to be drips of water at any time if it was split, or would all leaking water evaporate, even when cold? There's no dripping to be seen. I've had the cover off the boiler to look for any signs of a leak anywhere.

    Yes, I was told those valves would probably start leaking if touched. What do you suggest as best to isolate the heating?
     
  5. silver50

    silver50

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    I accessed the heat exchanger just now to try and inspect it. Here's a couple of pictures. One is showing some rusting at the right hand side front of the heat exchanger (the rust of course being mainly on the mild steel heat shielding) and the other is worse looking rust/debris etc which (perhaps exactly reflecting what you say Ian) at the lower rear left hand side of the heat exchanger.

    This seems to more than suggest leaking water certainly. As per my above question, would I be likely to see water dripping or drops, for example just now when it's cold? All looks dry. Thanks
     

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  6. ianmcd

    ianmcd

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    yes as suspected your heat exchanger is indeed goosed and that is the cause of your pressure loss, you will need new insulation panels too
     
  7. terryplumb

    terryplumb

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    On an 18 year old boiler ,dont waste your money replacing any of those ,but put the money towards a new boiler.
     
  8. silver50

    silver50

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    Thanks. Hopefully some progress at least.

    This boiler is miles away from a drain. I actually installed a grundfos pump a few months ago in anticipation of fitting a new boiler but it's hose is running a mile across my loft and feels less than ideal. Heating is all 8mm pipework too so I was thinking of complete relocation of the boiler and new pipework/radiators. Unfortunately my current kitchen and bathroom need to come out to locate the boiler where I'd like! Fine when the time comes but I need a building warrant for the work hence would have liked it if the old girl could be made to soldier on for another 4-5 months. I'll try to check price of the heat exchanger.
     
  9. There around £200 (new) and available, purchased one last week. The insulation panel (which has been soaking up the water leak) should also be exchanged. Not sure if they are available but first ask your gas technician if he is ok exchanging the heat exchanger and any other necessary parts,remembering its not cheap and you still have an 18 year old combination boiler.

    From the photos the corrosion on the side panel is a concern,it needs onsite inspection.

    :cautious:
     
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  12. Just leave it til its ****ing thru the ceiling
     
  13. terryplumb

    terryplumb

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    Or all over the floor and the flat belows ceiling .
     
  14. silver50

    silver50

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    Checking the price of a heat exchanger is not the same as saying that’s happening. To be honest I wouldn’t mind seeing a bit H2O dripping to feel totally confident about what’s been going on.

    I think a few replies are a bit unfair in light of me explaining why I’d like to try and make do with this (otherwise functioning fine) old boiler for a little bit longer. Installation of a new boiler is hardly cheap if it’s only to stay in that position until spring 2019.

    Thank you for the input though including on condition of the heat shielding.
     
    Last edited: 25 Nov 2018
  15. ianmcd

    ianmcd

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    I work on Vokeras mostly and you dont always see any water dripping as it sometimes only leaks when the burner is alight as the pressure increases and the heat exchanger expands, but trust me that heat exchanger is leaking, and the insulation pads are still available, if you are looking to have the boiler re-located though , I would recommend replacing it I wouldn't pay the expense to move that one. You mention needing some kind of building warrant, why is that ? I cover Edinburgh and only time I have come across that is on listed buildings
     
  16. silver50

    silver50

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    Hi, I wasn't meaning moving the existing boiler. I was meaning not wanting to replace it with a new one now only to have to move the new one next year.

    I'm seriously considering a complete switch around of kitchen/livingroom and bedroom locations. Building warrant for that and moving boiler/renewing heating when that got done.

    Thanks re the leak. It strikes me as just that, only when system on and hot that some water must be escaping. It very much looks like this must be the case because there really wasn't any sign of dripping water/water staining. Not sure what the insulation material is but it is actually all intact despite bits of rust on the metal backing.
     
  17. ianmcd

    ianmcd

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    you dont see staining or dripping as the water evaporates and is passed through the flue as steam, and you do need new insulation panels, the condition of the metal side cheek is a worry too and could possibly make your boiler immediately dangerous but without seeing it I couldnt be certain
     
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