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Thread: How do you drain down a sealed central heating system?

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    Should Get Out More Taipan's Avatar
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    Question How do you drain down a sealed central heating system?

    I want to flush out my system and top up with inhibitor etc, but how do you do this on a sealed system such as a combi boiler one?
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    Should Get Out More Yambo's Avatar
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    Default Re: How do you drain down a sealed central heating system?

    Find the lowest radiator and take off one of the pipes.

    Worked for me.

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    Default Re: How do you drain down a sealed central heating system?

    Find the bleed valve, it should be under one of the downstairs radiators.
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    Should Get Out More Taipan's Avatar
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    Default Re: How do you drain down a sealed central heating system?

    Quote Originally Posted by go_slow View Post
    Find the bleed valve, it should be under one of the downstairs radiators.
    There is a drain valve below the hall radiator but how do i flush the system out? Do I open the fill valve on the boiler whilst the drain valve is open?
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    Default Re: How do you drain down a sealed central heating system?

    Quote Originally Posted by Taipan View Post
    There is a drain valve below the hall radiator but how do i flush the system out? Do I open the fill valve on the boiler whilst the drain valve is open?
    No, flushing a system is not that easy. Seriously. You can just run the water in and out but that aint going to do anything except take time. If the system needs doing get a plumber to do it, they'll have the kit to flush it properly and then refill with inhibitor. I'll go find my plumbers website, it lists all the chemicals he uses and the tool he has, this is what your plumber should be using or similar for a good result.

    If you just want to put inhibitor in thats straight forward but a flush of the system isnt.
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    Default Re: How do you drain down a sealed central heating system?

    We have two little "taps" at the bottom of the system that poke out of the WC wall into the garden. made it easy for the guys who fitted a new boiler last year - worth checking if you have these coming off of the lowest bit somewhere.
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    Should Get Out More Taipan's Avatar
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    Default Re: How do you drain down a sealed central heating system?

    Quote Originally Posted by go_slow View Post
    No, flushing a system is not that easy. Seriously. You can just run the water in and out but that aint going to do anything except take time. If the system needs doing get a plumber to do it, they'll have the kit to flush it properly and then refill with inhibitor. I'll go find my plumbers website, it lists all the chemicals he uses and the tool he has, this is what your plumber should be using or similar for a good result.

    If you just want to put inhibitor in thats straight forward but a flush of the system isnt.
    Aye, i know it isn't straightforward but it obviously can be done. And i reckon I'm just the man to do it. I d'ont want to risk ruining my 25 boiler though, so perhaps I should get someone in, or just leave it as is (more likely).
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    Default Re: How do you drain down a sealed central heating system?

    Quote Originally Posted by Taipan View Post
    Aye, i know it isn't straightforward but it obviously can be done. And i reckon I'm just the man to do it. I d'ont want to risk ruining my 25 boiler though, so perhaps I should get someone in, or just leave it as is (more likely).
    here ya go

    Ultimate Handyman: diy powerflushing

    and after you have read that I suspect 'so perhaps I should get someone in, or just leave it as is (more likely).' is the right answer

    er what 'problem' are you trying to solve by flushing the system anyway?
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    Default Re: How do you drain down a sealed central heating system?

    Quote Originally Posted by Taipan View Post
    Aye, i know it isn't straightforward but it obviously can be done. And i reckon I'm just the man to do it. I d'ont want to risk ruining my 25 boiler though, so perhaps I should get someone in, or just leave it as is (more likely).
    Okie dokes, well if you want to flush it you simply need somewhere for the water to go in and somewhere for it to come out, breaking the connection to the pump on the boiler is the best, connecting the water direct to the tap is okay but just be careful of th water pressure since the closed cicuit system normally runs at a lower pressure then domestic mains.

    Close all the radiators, flush water in and see that it comes out clean. Open the inlet to the first rad and drain the air from it, then open the outlet. Repeat until water runs clear. Repeat for all rads.

    Put in inhibitor as per instructions (some go in neat, some need to be diluted). Reconnect the pump and fill the system.
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    Should Get Out More Taipan's Avatar
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    Default Re: How do you drain down a sealed central heating system?

    Quote Originally Posted by pistonbroke View Post
    here ya go

    Ultimate Handyman: diy powerflushing

    and after you have read that I suspect 'so perhaps I should get someone in, or just leave it as is (more likely).' is the right answer

    er what 'problem' are you trying to solve by flushing the system anyway?
    No problems with it, but thought it might be pruddent to flush and refill with fresh etc. I took a rad off recently to wallpaper and the water that came out was really black.
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    Default Re: How do you drain down a sealed central heating system?

    Quote Originally Posted by Taipan View Post
    No problems with it, but thought it might be pruddent to flush and refill with fresh etc. I took a rad off recently to wallpaper and the water that came out was really black.

    hmmm, 'if t'aint bust, don't fix it' would be my advice, but each to their own
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    Should Get Out More Yambo's Avatar
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    Default Re: How do you drain down a sealed central heating system?

    Quote Originally Posted by Taipan View Post
    No problems with it, but thought it might be pruddent to flush and refill with fresh etc. I took a rad off recently to wallpaper and the water that came out was really black.
    I suppose someone should tell you that the inhibitor that's already in the system could be black.

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    Default Re: How do you drain down a sealed central heating system?

    Quote Originally Posted by Taipan View Post
    I want to flush out my system and top up with inhibitor etc, but how do you do this on a sealed system such as a combi boiler one?
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    Default Re: How do you drain down a sealed central heating system?

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