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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
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    • CommentAuthorowlman
    • CommentTimeAug 4th 2019
     
    I was going to name this thread aquatic short circuit because that appears to be what's happening.
    Yesterday the kitchen hot water tap just wouldn't run hot despite there being plenty of hot water in the cylinder.

    System design:-
    Pressurised Solar thermal cylinder with usual bottom cold mains feed and top hot outlet distributed to various taps, bathroom, guest cloakroom, utility, and kitchen.
    All taps are Monoblock of one description or another so the only hot and cold mixing occurs at the tap end of each leg.
    Hot and cold are both pressurised so how come there could be any sort of "short circuit". Indeed the heating occurring in the solar cylinder would indicate that the hot may be marginally at a greater pressure than the cold, more than likely leading to taps favouring the hot side of supply, I guess.

    All have worked perfectly for years.

    I'm slowly going round the various taps to try and isolate any crossover which may affect the whole system.

    Has anyone come across this sort of thing before?
    :confused:
    • CommentAuthorMike1
    • CommentTimeAug 4th 2019
     
    Maybe you have a thermostatic mixer or non-return value that's failed? Or maybe a blocked filter in the tap connection / on the value input?
  1.  
    Ours did that, a bit in the tap mechanism had sheared so that turning the handle didn't operate the hot valve any more, a replacement cartridge was a few quid from Screwfix.

    But are you sure that's where the problem is? Do the other taps run hot? If you have isolating valves under the kitchen sink, you can disconnect the hot feed and run it into a bucket (or swap it for the cold feed to the tap) to check that hot water can get to the kitchen or not.
    •  
      CommentAuthordjh
    • CommentTimeAug 4th 2019
     
    Posted By: WillInAberdeenIf you have isolating valves under the kitchen sink

    And if you don't then turning the water off, disconnecting the tap and fitting isolators seems like a good move at this point :bigsmile:
    • CommentAuthortony
    • CommentTimeAug 4th 2019
     
    Does the hot have a pressure reducing valve?
    •  
      CommentAuthordjh
    • CommentTimeAug 4th 2019
     
    Posted By: tonyDoes the hot have a pressure reducing valve?

    Isn't it normal to put a pressure reducing valve on the cold main so the pressure to hot and cold taps remains balanced? That's certainly how ours is done.
    • CommentAuthorowlman
    • CommentTimeAug 4th 2019
     
    Thanks all for your replies:

    Mike1; Not long ago I installed a new thermostatic bath/shower mixer, I'll check that out.

    W i A : All my taps have isolators, so checking and pinpointing the culprit is my next step.

    djh and tony: I just had a thought that it may well be pressure differential. We have two rising mains in the property, both from the same house meter in the street but split, one in the utility for utility and kitchen taps, and the other which feeds the Solar cylinder and hot feeds and bathrooms, in the plant room. Only one, the plant room, has a PRV. So mains fluctuation/differential could be a culprit or at least one bit of the problem possibly combined with a slightly dodgy cartridge.
    • CommentAuthortony
    • CommentTimeAug 4th 2019
     
    I am suspecting a bypass through the cold tap and back into the hot pipe, try running hot in the kitchen with the cold shut off
    •  
      CommentAuthordjh
    • CommentTimeAug 4th 2019
     
    Posted By: owlmanI just had a thought that it may well be pressure differential. We have two rising mains in the property, both from the same house meter in the street but split, one in the utility for utility and kitchen taps, and the other which feeds the Solar cylinder and hot feeds and bathrooms, in the plant room. Only one, the plant room, has a PRV.

    That sounds like it might cause a problem as Tony says. The PRV should be on the rising main before it splits, so all the water in the house is at the same pressure. Put it just after the stopcock.
    • CommentAuthorowlman
    • CommentTimeAug 4th 2019
     
    The split is underground, Dave, so it's another PRV in the utility. That's going to be a heap of fun as the pipework is awkward to get at.
    Why is it when you find a solution, it's invariably in a bitch of a spot to get at. One of these bug...rs must be to blame. Possibly number 4.

    Murphy's First Law: Anything that can go wrong will go wrong.

    Murphy's Second Law: Nothing is as easy as it looks.

    Murphy's Third Law: Everything takes longer than you think it will.

    Murphy's Fourth Law: If there is a possibility of several things going wrong, the one that will cause the most damage will be the one to go wrong.

    Corollary: If there is a worse time for something to go wrong, it will happen then.

    Murphy's Fifth Law: If anything simply cannot go wrong, it will anyway.

    Murphy's Sixth Law: If you perceive that there are four possible ways in which a procedure can go wrong, and circumvent these, then a fifth way, unprepared for, will promptly develop.

    Murphy's Seventh Law: Left to themselves, things tend to go from bad to worse.

    Murphy's Eighth Law: If everything seems to be going well, you have obviously overlooked something.

    Murphy's Ninth Law: Nature always sides with the hidden flaw.

    Murphy's Tenth Law: Mother nature is a bitch.

    Murphy's Eleventh Law: It is impossible to make anything foolproof because fools are so ingenious.

    Murphy's Twelfth Law: Whenever you set out to do something, something else must be done first.

    Murphy's Thirteenth Law: Every solution breeds new problems.

    Murphy's Fourteenth Law: If anything can't go wrong on its own, someone will make it go wrong.
    •  
      CommentAuthordjh
    • CommentTimeAug 4th 2019
     
    Posted By: owlmanThe split is underground, Dave, so it's another PRV in the utility.

    Ah, we have a single length of pipe from the water board's meter to our stopcock and thence to the PRV. No underground fittings or anything to go wrong. Actually, thinking about it that's not quite true. The supply pops up in the garage first and is teed off to provide a supply there before it comes to the house. But no underground fittings. Might still be subject to the eleventh law of course :devil:
  2.  
    For hygiene reasons, the hot shouldn't be able to get into the cold and vv (eg in case the central heating system coils leak into the hot water cylinder, thence into the cold drinking water). Our mixing taps actually have separate h and c flow paths all the way to the spout, granted the shower doesn't.

    If you have two mains supplies with two stopcocks, one each supplying h and c to the kitchen, it sounds like you can easily work out which one is the problem....

    Murphy's law is a special case of the Second Law of Thermodynamics, which says entropy always increases and how much you must work to reduce it.
    • CommentAuthorowlman
    • CommentTimeAug 5th 2019
     
    <blockquote><cite>Posted By: WillInAberdeen</cite>For hygiene reasons, the hot shouldn't be able to get into the cold and vv (eg in case the central heating system coils leak into the hot water cylinder, thence into the cold drinking water). Our mixing taps actually have separate h and c flow paths all the way to the spout, granted the shower doesn't.

    True, but with many modern mono-block mixers the mixing occurs directly after the ceramic cartridge which is often only creating the required seal with an "O" ring.
    With single lever action taps that mixing can be potentially even more tenuous as that single lever opens and closes one or the other of either supply ports at the same time
    • CommentAuthorMike1
    • CommentTimeAug 6th 2019
     
    Posted By: WillInAberdeenOur mixing taps actually have separate h and c flow paths all the way to the spout, granted the shower doesn't.

    Many shower mixers have basic integral non-return valves to stop water flowing the wrong way. Though that doesn't replace the need for category 3 / 5 double check valves if the shower head is able to dangle close to water in basins / baths / WCs (see https://www.wras.co.uk/downloads/public_area/publications/general/prevention_of_the_risk_of_backflow_in_the_design_of_domestic_bathrooms.pdf/).
    • CommentAuthortony
    • CommentTimeAug 6th 2019 edited
     
    I have had troubles with water passing the tap and going backwards up the hot without coming out the spout once before

    Did you do the test with shutting off the cold and timing the hot with and without the cold on?
    • CommentAuthorowlman
    • CommentTimeAug 6th 2019
     
    Strangely tony it's righted itself although I suspect the culprit is the newest tap which I fitted when I refurbished my kitchen 18 months ago. It's a SS single lever monoblock job from a reputable manufacturer, or should I say supplier as none of them actually seem to do any manufacturing. That process seems to be in a nether world of anonymous worldwide factories, so getting anywhere with a solution is beyond reach of mortals.
    The sad bit is it's fitted direct into the granite worktop at the rear of the inset sink and replacing it would be a dog of a job. So it's watch and wait and hope.
  3.  
    Perhaps a blockage somewhere that has now shifted either out through the tap or hiding, waiting to strike again
    • CommentAuthorowlman
    • CommentTimeAug 6th 2019 edited
     
    Yes, like a Ninja, Peter:wink::bigsmile:
    • CommentAuthortony
    • CommentTimeAug 6th 2019
     
    I hate it when that happens as you never know what was causing it.
    •  
      CommentAuthordjh
    • CommentTimeAug 6th 2019 edited
     
    Mike1 posted: https://www.wras.co.uk/downloads/public_area/publications/general/prevention_of_the_risk_of_backflow_in_the_design_of_domestic_bathrooms.pdf

    Thanks for that link. I hate those rings that constrain the shower hose, so took the one off in our ensuite. Then the plumber came back with his inspector (he made our house a sample for his inspection) and put it back through the ring again. He did apologize. So after he'd gone I took it out again. :devil: Now I know his inspector was wrong to insist, since the shower is way too far from the WC and basin and there's no bath. Plus IIRC we have non-return check valves anyway. :bigsmile:
    • CommentAuthorMike1
    • CommentTimeAug 8th 2019
     
    Posted By: djhThanks for that link. I hate those rings that constrain the shower hose
    Me too - I much prefer appropriate check valves.
  4.  
    Just for clarity of future searches, double check valves are only legal for preventing contamination from baths and basins getting via the shower head into the clean water supply - it would be illegal to rely on them if the shower hose is long enough to reach the WC. It's criminal (not civil) law. The double check valves obvs have to be located in the shower supply piping, downstream of the tee off from the piping to basin (drinking) taps, IE double check valves on the incoming mains or at the hot water cylinder wouldn't help.
  5.  
    Going back to the original problem - Could the problem have been an air lock in the pipe?
    • CommentAuthorowlman
    • CommentTimeAug 9th 2019 edited
     
    I suppose it could be, Peter, but not in this case. I'm sure the problem is one particular tap, the newest and most expensive as it happens. It's to do with the odd, figure of eight shaped "O" ring at the base of the ceramic cartridge. The even more odd shaped retaining nut which tightens the "O" ring against its seating is really bloody difficult to tighten with no special spanner supplied, a glaring design error IMO.

    P.S. I think I'll end up making a box spanner myself, when I find time.
    • CommentAuthorMike1
    • CommentTimeAug 9th 2019
     
    Posted By: WillInAberdeendouble check valves are only legal for preventing contamination from baths and basins getting via the shower head into the clean water supply - it would be illegal to rely on them if the shower hose is long enough to reach the WC. It's criminal (not civil) law.

    Indeed; as per the document I linked to above, If the WC is within the zone of backflow risk of the shower hose, the hot and cold water supplies to the shower combination tap must be protected by a fluid category five backflow device.
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