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Green Building Bible, Fourth Edition
Green Building Bible, fourth edition (both books)
These two books are the perfect starting place to help you get to grips with one of the most vitally important aspects of our society - our homes and living environment.

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  1.  
    When was the safety cutout in your immersion checked last?

    Immersion heaters are supposed to have a 'dual safety' cutout that pops out if the water gets dangerously hot, as a backup if the thermostat malfunctions. There have been a small number of fatal scalding accidents when systems boiled over.

    Our annual boiler service didn't go anywhere near the cylinder, so I had a look and found:

    - the immersion thermostat doesn't have a cutout at all

    - a separate cutout is fitted in the immersion but is so corroded up it doesn't work anymore

    - the immersion was factory-fitted by a well known UK cylinder manufacturer in 2009


    I bought a new dual-safety thermostat from a national chain. The cutout is supposed to pop at 90degC but it didn't open when tested in a boiling kettle. Tested in the oven, the cutout operated at 107degC, which seems useless to prevent the system boiling or scalding.

    I'm pretty unimpressed that a) the factory-fitted cutout failed silently while not particularly old, b) the annual services didn't fix it, and c) the new thermostat looks great but doesn't protect us at all.

    Please everybody check that your immersion cutout works!



    https://www.hse.gov.uk/services/localgovernment/hotwatersystems.htm#
    • CommentAuthorowlman
    • CommentTimeJun 8th 2020
     
    I think most run of the mill domestic immersion heaters have their thermostat right next to/in the middle of the elements, and it's what most cylinder manufacturers fit. Surely it would be better to have the stat, or two, in separate pockets, and linked to an independant controller. All down to cost I guess.
    I recently fitted a 6kW (2 x 3kW) immersions in my large accumulator tank, I had them fabricated for my specific needs, length etc., and was offered variations of controls as well as different element types.
    • CommentAuthorborpin
    • CommentTimeJun 8th 2020
     
    Posted By: owlmanI had them fabricated for my specific needs,
    Where did you find someone to do that?
    • CommentAuthorEd Davies
    • CommentTimeJun 8th 2020
     
    borpin: “Where did you find someone to do that?”

    Dunno where Owlman went but the first place I'd try would be http://www.tpfay.co.uk/ .

    Paul at the end of the road has used them, IIRC.
    • CommentAuthorowlman
    • CommentTimeJun 8th 2020
     
    I did contact the one Ed mentioned, I may even have got a quote from them, plus others. Most of the firms in this line of work I think are reputable and offer a good range of variants. I eventually went with this company.

    http://www.midlandelements.co.uk/
    •  
      CommentAuthordjh
    • CommentTimeJun 8th 2020
     
    But do check before testing that your cutout is of the type that can be manually reset. Some are not resettable and must be replaced if they operate.
  2.  
    I did look at those, but after my experience with both the factory-fitted and replacement safety devices both being duds, I won't trust a cutout that cannot be tested at regular intervals through its lifetime.

    Owlman, out of interest did you test the thermal cutouts when you comissioned your immersions? Do you know that they work at the right temperature?
    •  
      CommentAuthordjh
    • CommentTimeJun 8th 2020
     
    Posted By: WillInAberdeenI did look at those, but after my experience with both the factory-fitted and replacement safety devices both being duds, I won't trust a cutout that cannot be tested at regular intervals through its lifetime.

    Just out of curiousity - do you test your RCDs and fire alarms? I can't say I do it as often as I'm supposed to.
  3.  
    Our toaster tests the smoke alarm and the RCD pretty much weekly, whenever somebody tries toasting their hot cross bun....

    I checked the expansion vessels but haven't found a meaningful way to test the pressure safety valves.
    • CommentAuthorowlman
    • CommentTimeJun 8th 2020 edited
     
    The 2 x 3kW 230V immersions, in one pocket, are located roughly in the centre side, of a 2000L accumulator. They are independently wired in preparation for two single phase Solar divereters from a 10kW array.
    The 2 stats for this array are located above and below the immersions and eventually when connected to a control, as yet to be designed, will act as cutout for the whole thing. However, with 2 tonnes of water I doubt that any stat will ever get a chance to operate.
    In practice this Solar PV input will only operate as top up for log biomass in the shoulder and winter months as I have Solar thermal for Summer use.
    • CommentAuthorowlman
    • CommentTimeJun 8th 2020
     
    Posted By: WillInAberdeenOur toaster tests the smoke alarm and the RCD pretty much weekly, whenever somebody tries toasting their hot cross bun....

    I checked the expansion vessels but haven't found a meaningful way to test the pressure safety valves.




    I've just recently changed the combination pressure /temp safety valve on my solar thermal cylinder. I realised something was wrong when the tundish overflow started dripping for no reason.
  4.  
    Just as an aside - a couple of years ago, during one of the heat waves, my Solar thermal got the Hot water jolly hot - somewhere close to 80C.
    This tripped the safety stat which was set to minimum - about 65C, I'd guess. It'd been like that since installation, 10+ years ago. So the boiler wouldn't switch back on until I'd worked out what had happened.
    Manual reset and adjustment and all good.
  5.  
    So I bought another dual-safety thermostat, this time a branded one (Backer BMST) from a specialist seller on eBay. Tested it in the oven and it cutout within a few degC of specified temperature. Slightly bigger than previous one but shoehorned it in. Will test it again in a couple of years.
    • CommentAuthorcjard
    • CommentTimeJun 15th 2020
     
    > Our toaster tests the smoke alarm and the RCD pretty much weekly

    How does a toaster that succesfully operates the RCD then test the smoke alarm?!

    >the cutout operated at 107degC

    Don't forget, that water under pressure has a higher boiling point.. The problems would probably come when you open a tap and release the pressure..
  6.  
    Our kids toast many hot cross buns:
    Stray crumbs -> burn -> sets off the smoke alarm
    Stray raisins -> moist -> shorts element -> trips RCD
    Not usually both from the same hot cross bun!

    (There's a joke about residual currants in there somewhere)


    107degC:
    Those dual safety stats are also used in open vented systems, see the link in OP about fatal boiling-over accidents in vented systems, so they are dangerous if they don't work at the advertised temperature. Ours is an unvented system, but we don't want boiling water coming out of sink taps. (Edit: or the temperature safety valve to dump boiling water)
    • CommentAuthorEd Davies
    • CommentTimeJun 15th 2020
     
    Posted By: WillInAberdeen(There's a joke about residual currants in there somewhere)
    :bigsmile:
  7.  
    So a year has gone by and the boiler service was due again. After last year's debacle with the 'heating engineer' who didn't check the pressure safety valves or the immersion safety cutout, he was not invited back, and a different firm were called.

    Their man also didn't show any interest in safety devices outside the boiler cabinet. After some prompting he agreed to come upstairs to eyeball (literally) the CH safety valve and expansion vessel. These sit adjacent to the DHW temperature/pressure safety valve and the immersion cutout, but he couldn't be persuaded to take any interest in those - hot water safety is apparently for mere plumbers, and he had progressed up the ranks to be a boiler man.

    Has anyone ever managed to get an annual service done, which has actually checked their immersion cutout is still working? Or their cylinder safety valve?
    • CommentAuthorjms452
    • CommentTimeJun 22nd 2021
     
    Posted By: WillInAberdeenHas anyone ever managed to get an annual service done, which has actually checked their immersion cutout is still working? Or their cylinder safety valve?


    I guess it depends what the service is for... We have a boiler service rather than a full plumbing and hot water check the first is less £100, the later - i dread to think.

    Our PV diverter checked the safety thermostat when I turned the immersion thermostat up above about 85C but it was a premium Backer one. Now turned down to a more modest value.
  8.  
    Posted By: WillInAberdeenHas anyone ever managed to get an annual service done, which has actually checked their immersion cutout is still working? Or their cylinder safety valve?

    The only way I can think of testing either of the items would be to remove them from the system and subject them to a temperature / pressure test using the appropriate test equipment - I can't see that happening.....ever.
    Any one know of an in-situ test for these items?
  9.  
    Good question!

    For the immersion, if the previous 'engineer' had just removed the cover (one screw), it was immediately visible that the OEM's safety stat was all corroded and seized shut.

    If he had withdrawn the replacement stat (two screws) and dunked in some boiling water, it would have been obvious that it didn't work.

    For the pressure safety valves, he could have turned the knob and watched the tundish flow to see they weren't seized shut. Agree that it's hard to check the temperature/pressure setting is correct. Perhaps pressurise the whole system and check the valve opens at the required pressure, but could cause problems if it didn't...

    For the expansion vessel, he could have checked the precharge with a tyre pressure gauge after running off some hot water.

    I can do these myself but I imagine most folks don't, especially if a 'heating engineer' has just given them a certificate saying that the system is all safe, without having checked any of this! I had never thought about it until reading about the injuries the little girl had who died, truly horrendous accident.
    •  
      CommentAuthordjh
    • CommentTimeJun 23rd 2021
     
    I'm glad at least that my system is at atmospheric pressure, apart from the mains water itself. :) No safety valves or expansion vessels to check.
  10.  
    Sounds good, but the fatal accidents were also with open vented systems. The immersion boiled the water in the system, the heat caused plastic components to fail, then the boiling water fell through ceilings onto the victims.
    • CommentAuthorDavidND
    • CommentTimeJul 2nd 2021 edited
     
    <blockquote><cite>Posted By: WillInAberdeen</cite>
    Those dual safety stats are also used in open vented systems, see the link in OP about fatal boiling-over accidents in vented systems, so they are dangerous if they don't work at the advertised temperature. Ours is an unvented system, but we don't want boiling water coming out of sink taps. (Edit: or the temperature safety valve to dump boiling water)</blockquote>

    It was after a couple of children were scalded to death that the regs were changed so that all immersion elements since must have a cut out. However, the reg was NOT retrospective.

    Re unvented cylinder servicing.
    There is a T & P (temperature & pressure relief safety valve) which 'goes' at approx 8 bar & between 90 & 95 degrees Centigrade so you will never get boiling water from a tap!

    For everyone's information, a GasSafe registered plumber is NOT qualified to do unvented cylinders UNLESS they have a dedicated card to demonstrate they know what they are doing. Never let anyone touch your unvented cylinder if they can show you they are qualified. They will have a small card showing their G3 qualification.

    It is NOT normal practise to check thermostat cut out operation btw. Much as I might like to do it, people simply do not wish to pay for it!

    All proper G3 engineers will check the expansion vessel. They are the primary weak point as the rubber bladders are gas permeable meaning they lose charge over time which increases system pressure overall and causes more problems. The precharge pressure is calculated not guessed.
  11.  
    I understand but cannot agree with that position. Similar excuses were rolled out by the plumbers at the inquest into the little girl's death in 2006 from a faulty stat without a cutout. (Along with "we didn't check it because we didn't have a ladder"). At that time, they already knew that safety cutouts are required.

    https://www.dailymail.co.uk/news/article-506604/Water-tank-fault-scalded-baby-girl-death-known-unreliable.html

    If I paid a garage to service my 10 year old car, and later found out that the brakes were faulty but they hadn't checked them, because "we don't normally do that" or "people don't want to pay" or "we don't have the right certificate" or "they are not retrospective" or "the handbrake will protect you if the brakes fail" - then I'd never go back!

    If I found that the whole garage industry seem to find this
    attitude acceptable, and that the replacements sold by a major national chain don't work, then I'd be making a fuss! And advising others to make sure their safety devices have been adequately tested.

    BTW G3 is part of the English building regs, we have something different here. G3 doesn't allow you to rely solely on the t/p safety valve, you need a working cutout as well. Our t/p valve was fitted in the same factory as the long-since-failed safety cutout, and seems not to have been checked since, so I have very little confidence that it would still open at the required setting.
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