Many posts to this forum are about how to clear pipes - this one is about how to block one!

I have a cold water header tank in my attic, there's a short length of pipe that feeds from this tank to the hot-water tank in the airing cupboard below. The pipe is (I think) steel and appears to be BSP threaded 1 inch pipe. The pipe is corroded, and attached to a brass gate-valve that's been seized for many years. The pipe then converts to 22mm copper pipe before getting to the hot-water tank.

I'd like to replace the seized gate valve, and since I'm comfortable plumbing with copper pipe the simplest option (for me) seems to be cut a new hole in the tank, fit a new 22mm compression tank-connector, and then re-plumb from there to the hot water tank.

The old tank connector appears to be steel and is very rusty, I'm also pretty sure that any attempt to remove it to re-use the hole would fail, and would probably damage the tank in the process.

Bearing this in mind, I'd like to cut-off the existing pipe 6 inches from the tank and simply block it up. What's the best way to do this? I've not worked with steel pipe and don't have access to threading equipment. Since the pressure at this point is equal to the height of water in the tank, it's doesn't need to be a very sophisticated solution. Is there a reasonably reliable of blocking such a pipe?


  • Can you remove the old outlet altogether and replace it with a compression fitting that you glue a cap to?
    – Zach
    Apr 1, 2020 at 20:23
  • Did you ever get this resolved? If so, please give a check-mark to the answer that helped you the most, or write up your own answer explaining what you did to get it fixed and give yourself a check mark. That will help others with this kind of problem know that this has a resolution and is a good place to look for their answer.
    – FreeMan
    Aug 31, 2020 at 12:43

2 Answers 2


Marine epoxy will plug a hole that size, I would plug the pipe an inch back fill or pack the hole with marine 2 part epoxy and fill the hole we did this for an emergency repair on a boat and it held the entire week we were offshore.

  • 1
    It sounds like this is part of his potable water system. Is marine epoxy known to be safe for drinking water?
    – Khrrck
    Apr 1, 2020 at 16:23

To answer your specific question:
I would cap it with a 1" galvanized steel cap secured with either Marine epoxy as suggested by Ed or another type of construction adhesive. Won't matter too much because the cap will be blocking flow rather than the adhesive.
Here's my concern:
If the current connector is as rusted as you say, it's only a matter of time before it's going to rust through and fail. You don't mention the material the tank is made of. If it's feasible at all I would remove the pipe and connector and find a reliable patch for the tank.

Here's a link to another possible solution for a cap if that's the way you decide to go.
plastic pipe cap A plastic cap that you can secure with a hose clamp for extra security.

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