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New Hot Water Cylinder but no hot water.

Discussion in 'Plumbing and Central Heating' started by DariusB, 5 May 2021.

  1. DariusB

    DariusB

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    Hi All,

    New to this forum so thanks for having me. I am completely DIY useless so bear with me!

    I recently had a leak in my hot water cylinder that needed replacing. The house was built in the late 70's and judging from the state of what was inside it it might have well have been the original one for all I know.

    Anyway, got a local plumber to come and fit a replacement, which he did, and took a lot less time than I expected. As he was walking out he said, hopefully it will work. When pushed by a slightly concerned me (had been out of hot water for a week and my wife was close to filing divorce papers), he said gravity fed systems were not really used any more and the new hot water tanks do not work in quite the same way.

    Anyway, I turned the water heating back on and soon after the pipe leading from that back up into the airing cupboard was getting hot so happy days I thought.

    Sadly my optimism lasted less than a few hours with the water in the tank getting no warmer than my wife's mood, so the hot water was obviously struggling to get up into the tank.

    Any ideas on a fix for this? The plumber has suggested maybe a small pump could help push the hot water up into the tank but said he would have to look into it?

    Thankyou!
     
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  3. oilhead

    oilhead

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    Current cylinders will not work on gravity hot water. You will need the system to be brought up to a fully pumped standard, either a Y plan, or S plan. Your plumber should really have known this and sorted it out before undertaking any work.
     
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  4. winston1

    winston1

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    Why not? What is different about them that stop them working?
     
  5. muggles

    muggles

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    If you've got a system which relies on gravity circulation, you need a cylinder which has a coil inside it designed to work in that way. They're still widely available either same day or next day at all good plumbers merchants but the correct cylinder must be used. Lobbing any old thing on there won't work as you've now discovered. Fully pumped cylinders use smaller bore tube in the heating coil, and often have rises and falls in the coil to maximise use of the available space. Gravity coils need large-bore smooth tube which descends continuously from the top (flow) connection to the bottom (return) connection.
     
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  6. dilalio

    dilalio

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    Would a 70's built house still have had a gravity HW system?

    OP, what boiler do you have?
     
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  7. muggles

    muggles

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    Potentially 50 years old, I'd say it's certainly possible
     
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  8. Dangee

    Dangee

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    Could you post a couple of photos?
     
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  9. winston1

    winston1

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    Thanks for that. Never realised special fully pumped cylinders existed. You learn something every day.
     
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  11. RayCaister

    RayCaister

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    My 1978 3 bed detached new build had a Ideal Concord WRS255 with pumped C/H and gravity H/W. The whole system was still going strong without any major repairs or servicing when I sold it 35 years later.
     
  12. CBW

    CBW

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    I think you’re getting confused. Yours sounds fully pumped, as in the heating of the water inside is fed by a pump. My current 2010 build has gravity fed hot water, but the heating of the cylinder is pumped. We’re talking about the gravity heating of the cylinder, by means of heat rising and cooling water (convection) circulating by gravity only.
     
    Last edited: 6 May 2021
  13. DariusB

    DariusB

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    Thanks for your many replies - I appreciate you taking the time. The Boiler is a Johnson & Stanley Hi Spec J25 System E-T which also runs the heating via a slightly antiquated warm air system, but it does the job.

    The plumber is usually very reliable/experienced and one we have used previously several times so I still find it all slightly strange. He said that there were new regulations introduced a few years back so they were not allowed to install a gravity tank?

    Rightly or wrongly the tanks in there now - would a small pump pushing the hot water up to the tank work do you think / any suggestions, etc. I don't have a pool of money right now to do anything major unfortunately.

    Will upload some pictures below as requested.
     

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  14. muggles

    muggles

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    It's quite common for older boilers like this to have pumped CH and gravity circulated hot water Chris.
     
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  15. muggles

    muggles

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    Your options would be to either replace the cylinder with one of the correct specification, or fit a timer, cylinder thermostat, and circulation pump. I'd suggest that as your installer has mis-specified the original cylinder, it's up to them to replace it with the correct one free of charge.
     
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  16. RayCaister

    RayCaister

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    A more technical answer would have been that the unpumped heated water from the heat exchanger in the boiler was lifted by thermal efficiency to the immersion tank upstairs directly above. As a small benefit it also provided a little flow to the upstairs radiators.
     
  17. JohnD

    JohnD

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    but a better solution would surely be to convert it to fully pumped.

    my old mum had a gravity circ cylinder which was very slow to heat, and uneconomical in summer as it relied on the timer and boiler stat. converting it to pumped fixed both those.

    it also shifted a lot of sediment out of the pipes and coil, which showed in the Magnaclean.
     
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