Draining completely isolated hot water cylinder

Discussion in 'Plumbers' Talk' started by PhilRogers, Oct 31, 2019.

  1. PhilRogers

    PhilRogers New Member

    I have an old, disused, hot water cylinder in a cupboard in my (downstairs) dining room (!) installed by the house's previous owners.
    It has been isolated from the cold water supply in the roof, and the hot outlet pipes have been capped off in an unknown place, somewhere under the upstairs floorboards.
    As it is no longer in use, I want to remove the cylinder, but it appears to be still full of water.
    The cylinder has a drain cock at its base, so I connected a hose and jubilee clip to that, and opened the cock, but nothing comes out, except a few drops of water.
    I guess this is because the pipes connected to it are sealed off, so no air can get into the system.

    I tried unscrewing the immersion heater at the top of the cylinder, but because that simply caused water to come out of there because there's still water in the pipes leading from upstairs.
    Obviously, I want air to enter the system fro the highest point, which will be where the pipes are capped off, but as I mentioned, they are under the upstairs floor. I'd really like to avoid taking up the floors to find the pipes, so can anyone suggest a way of draining the cylinder without getting water everywhere, and without ripping up all my floors to find the ends of the pipes?

    By the way, the pipes that enter the cylinder are old iron pipes, so I cannot use a self-cutting T-connector to create a side-pipe that I can extend upwards to allow the air in.
     
  2. terrymac

    terrymac Well-Known Member

    The drain cocks washer is probably stuck in the closed position. Can you post pic of the drain cock ? If the drain cock is fully open ,loosen the immersion heater and water will flow out the drain cock.
     
  3. Joe the Plumber

    Joe the Plumber Well-Known Member

    Don't forget to take it to your local scrap metal merchants when you've got it out.
     
  4. PhilRogers

    PhilRogers New Member

    Some water comes out of the drain cock when I crack open the immersion heater, but it also comes out from around the immersion heater because of the head of water in the pipes above, so I had to close it again.

    And I have since discovered that the cold supply from the tank in the roof is still there and the stop-cock on that pipe has no handwheel and is stuck open.
     
    Last edited: Oct 31, 2019
  5. PhilRogers

    PhilRogers New Member

    Yes, I planned to do that as I also have some old lead flashing that I took off my old porch roof a few years back.
     
  6. PhilRogers

    PhilRogers New Member

    Just realised that the cold water supply, from the tank in the roof is actually still connected via a stop cock that has no handwheel on it, and doesn't budge with the mole grips either.
    I think the only way is to drain the cold water tank and let the air in that way, and blank off the outlet to the hot water cylinder before refilling the tank.
     
  7. terrymac

    terrymac Well-Known Member

    So the tank in the roof is still supplying / connected to ,the hot water cylinder??
    What else does the tank in loft supply ,how many outlets does it have at the bottom ?
    What currently heats and supplies your domestic hot water ?
    Sorry to ask so many questions ,but need to fully understand your set up in order to offer suggestions.
     
  8. Heat

    Heat Well-Known Member

    On cylinders that have no functioning, or no drain cock fitted I remove the top fitting and use a hose with a half metre of 15mm copper pipe pushed into hose to drop into bottom of cylinder and start a siphon
     
  9. PhilRogers

    PhilRogers New Member

    Yes, but the problem is that if I remove the top fitting, the water that is still in the pipes above the cylinder will leak out.
     
  10. Heat

    Heat Well-Known Member

    If you can isolate the cold pipe at cold tank that feeds the cylinder, or drain the cold tank, then usually when you open a hot tap below cylinder level then the cylinder will be full only to the top draw off.
    But there could be some water remaining above cylinder level if the draw off is high
     
  11. PhilRogers

    PhilRogers New Member

    Don't worry, questions are good.

    Yes, the cold water tank is still supplying the old cylinder, which is downstairs in a cupboard in the dining room.
    The same cold water tank supplies a new cylinder upstairs in the bathroom.
    There are 2 outlets at the bottom. One supplies the old cylinder, but the stop cock is jammed and has no handwheel on it. The pipe from the cylinder to the stop cock is copper (22mm or 28mm - I'm not sure) and the pipe that comes out of the stop cock is an old iron pipe that goes down to the cylinder.
    The other outlet supplies the new hot water cylinder.
    That new cylinder heats the domestic hot water.

    Thinking about it, the stop cock must be jammed closed, otherwise the water would flow when I open the cylinder drain.
     
  12. Joe the Plumber

    Joe the Plumber Well-Known Member

    If the 'stop cock' is a gate valve, it almost certainly won't work, regardless of how well turned off it appears to be.

    If you're lucky, the pipe feeding it from inside the cold tank will be connected to a tank fitting (on the cold tank)
    that is round inside. Stick a bung into this inside the tank and you can then disconnect the broken valve and cap off the outlet
    from the tank with a compression stop end (as close to the tank as possible). Bungs:

    https://www.toolstation.com/radiator-valve-change-kit/p31768

    This will leave the cylinder feed pipe open to let the air in to drain the cylinder.
     
  13. Mike58

    Mike58 Active Member

    Joe the Plumber likes this.
  14. Joe the Plumber

    Joe the Plumber Well-Known Member

    No problem with that. I was simply showing the OP what he could use. Even better perhaps, buy a decent bottle of wine with a cork...!
     
    Mike58 likes this.
  15. PhilRogers

    PhilRogers New Member

    Thanks for all your advice.
    I think I'll bung the hole in the tank and cut and cap off the outlet. Then I'll be able to drain the cylinder and all the connected pipes.
     
  16. Mike58

    Mike58 Active Member

    And that is a better idea, although after drinking the bottle I will be unable to remember where the cork is. Corks can be a little small, although if one fits, the sherry bottle type with a plastic head are better as easier to pull out.
     
    Joe the Plumber likes this.
  17. Heat

    Heat Well-Known Member

    If the hot outlet is capped off below upstairs floors, it might still have the vent pipe connected and still an open end in attic and cylinder would be able to draw air in.
    If cylinder drain cock was opening properly the water should still flow if feed pipe is open.
     
  18. PhilRogers

    PhilRogers New Member

    After a lot more investigation, I discovered that the pipe that I thought was supplying the old cylinder is not.
    It turns out that the cylinder is connected directly to the water main, presumable to ensure that there is a decent pressure for the hot water supply (because the cylinder is downstairs).
    Alarmingly, there is no expansion vessel, which means that the cylinder was at mains pressure with no means of pressure relief if the contents got too hot. I am so glad that we stopped using it!
    Unfortunately, the pipe that supplies the cylinder tees off somewhere under the upstairs floor, and also supplies the utility room where the washing machine is, so if I turn off that supply, the washing machine is out of action.
    I could install a new supply to the washing machine, but that will be a lot of effort, so I'm going to try to disconnect the cylinder supply and cap it.
    Unfortunately for me, the pipes are iron, which I've never really worked with, so I'm entering into a whole new world...

    We had a new gas fire fitted this week and I asked the engineer about the cylinder (which was in the same room ). He confirmed that the cylinder is still full and that the drain cock on it is very likely blocked with limescale, which explains why nothing is coming out of it.
    His suggestion is to disconnect the inlet pipe and then siphon the water out.
     
    Last edited: Nov 7, 2019
  19. Heat

    Heat Well-Known Member

    The cylinder being downstairs wouldn’t have caused pressure problems as it is the cold tank that gives head of water and therefore pressure.
    So the cylinder location was irrelevant.
     
  20. terrymac

    terrymac Well-Known Member

    What kind of cylinder is it ,can you post pics ?
    I still think the rubber washer is stuck in the drain valve ,seen it loads of times
    Is the cylinder copper ?
     

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