Today I drained my central heating/hot water system. This is a standard vented, pumped S plan with two electric valves and an indirect hot water cylinder, and I'm in UK.

I was lucky enough to have a drain valve underneath ground floor, relatively accessible, see pics:

enter image description here

So I opened it and was able to drain: good! However, upon refilling the system, I found out that that valve will rotate endlessly, and won't guarantee proper isolation: it's stripped.

I was thinking to add an isolating (aka service) valve past the old one, i.e., along the pipe in the bottom part of the images.

Something like this: enter image description here

Do you think that will work? Or is there a risk that the old valve will leak when the new one is shut? Do you foresee any other possible problem?

Any feedback welcome!


  • 1
    For those of us not in the UK, would you mind editing your post to describe what a "CH/HW" is. Also, did your work involve turning the valve in question, or was it left alone?
    – FreeMan
    Commented May 18, 2020 at 17:26
  • Thank you! I don't have an answer for you, but at least now I know what you're talking about.
    – FreeMan
    Commented May 18, 2020 at 17:40

1 Answer 1


Adding one of those isolators is a good plan.

I used to put one inline with every tap as they are cheap and make subsequent maintenance easy - less draining of the whole system.

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