I would like to temporarily remove this radiator to do some drywall and painting and during that time, I would like the rest of my radiators to operate normally. The elbows, which are essentially adapters between the radiator and the standard 3/4" galvanized pipe that supplies it water, consist of a main L body that fits onto the pipe as female, nut, and a nipple that fits into either the radiator itself, or as is the case here due to my specific case scenario, another 3/4" female as a male ("REGULAR GALVANIZED COUPLING" in the picture).

The way to detach the radiator is by loosening the nut, which leaves me, on the elbow side with the nut, and on the radiator side with an extension pipe that is joined with the elbow nipple using a regular 3/4" union (female on both sides). I am really trying to avoid removing the super short nipple from the union on the radiator side in order to mount a cap on it.

enter image description here

The logical choice would be a plug sized specifically to fit into the elbow nut, which is not 3/4" (slightly bigger). I went to a specialty plumbing store and they said such a plug does not exist but I find it hard to find. Does anyone know of a fitting that would singularly plug this radiator union? Such a fitting would go into the nut, instead of the ELBOW NIPPLE (picture) and there would be nothing to the left of it.

  • While I'm not surprised that there's not a plug for this, I find it hard to believe there's not a cap that could be screwed on that, with some thread tape, would perfectly seal this for 3 minutes or 30 years...
    – FreeMan
    Jan 24, 2023 at 15:29
  • Forgive my ignorance, but doesn't the hot water flow through the radiator? So both inlet and outlet would have to be capped? And if they were, wouldn't that stop anything downstream from heating?
    – beswald
    Jan 24, 2023 at 16:15

1 Answer 1


We did this a lot. Depressurise the system and drain to just below the working point.

Just get a spare nut and a suitable coin. We used 2 pence pieces as they fitted well. You can use any disc of metal which will fit - coins make a good substitute as they tend be available. Washers are round and usually a suitable thickness but the hole in the middle tends to spoil their effectiveness for this use 😀.

Wrap the 2p or equivalent metal disc with ptfe and then clamp up with the nut.

It is also possible to get cap nuts that fit - but they tend to be rare - I have a couple as I used them while decorating and rebuilding walls to get radiators out of the way, but not everyone has them available as the coin trick works too well.

Then refill and repressurise the system and test.

  • i don't understand what "coun" and "2 pence piece" are
    – amphibient
    Dec 24, 2022 at 17:11
  • They're suggesting a small disk if metal of the appropriate size. In their case, a two-pence coin was a good fit; whether a coin will work for you depends on the sizes of your local currency.
    – keshlam
    Dec 24, 2022 at 17:37
  • @amphibient a "2 pence piece" is a British unit of currency equivalent to a 2 penny coin if we had those in the US. (Note: equivalent, not equal - that depends on current exchange rates.)
    – FreeMan
    Jan 24, 2023 at 15:28

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