We have a pipe that bangs for a while right when we turn the heating on. I managed to isolate where the pipe is (under the floorboards on one room), the problem is that I can't lift the floorboards because they go under a built in wardrobe, and I don't want to cut them in case I hit the pipe.

I read that an idea could be make a hole on the floorboard right on top of the pipe (I'll need to figure out how to do it without hitting the pipe) and just inject insulation foam, but I'm not sure about this method.

Has anybody have any suggestion or similar experience?

  • Is the area around this pipe accessible from the ceiling or crawl space below?
    – Michael Karas
    Feb 5, 2020 at 14:36

2 Answers 2


You can control the depth of cut very accurately with a circular saw.

However, banging pipes are usually caused by water-hammer, and securing the pipes doesn't completely cure the problem. You (or a plumber) can install a shock arrestor (various types are available) near the valve that is causing the problem.

  • How can I be sure is water hammering? The banging starts some seconds after I turn on the heating and stops after around 30 seconds.
    – Antonio MG
    Feb 5, 2020 at 17:09
  • 1
    Still likely water hammer. It is making that noise because that's the first place where the pipes are loose enough to rattle.
    – JRaef
    Feb 5, 2020 at 19:57

"Water hammer" is the result of any sudden change in pressure or flow in a pipe. Liquids (water) don't compress or expand, so when there is a sudden change in pressure or flow, the kinetic energy of the liquid gets converted to an energy shock wave that travels up and down the pipes looking for a place to dissipate, in this case as mechanical movement of the pipes themselves, likely because of poor or old failing bracing. Injecting foam (more later) is only going to move the problem to some other area and likely make things WORSE.

The CORRECT way of dealing with this is to have some sort of "shock arrestor" installed in your piping system somewhere. This can be a complex device, or in many cases just a vertical pipe somewhere with air trapped in it, because air DOES compress. In some old houses where people have done modifications or additions, they find these old trapped air pipes, cannot figure out what they were for, then use them as "free connections" for the addition / modification and thus unwittingly remove their essential function. You need to make sure you have some form of water hammer suppression, otherwise the problem persists until a pipe bursts inside of the wall.

Injecting foam, aside from masking the issue instead of solving it, also runs the risk of damaging your floor. It can be VERY VERY tricky to make sure you don't inject TOO MUCH foam because if the space available is too limited for the amount of expansion it will have, you can end up with it blowing out your floorboards or the ceiling below, causing more problems than it solved. Resist the temptation for a quick fix...

  • Thanks, I won’t use the foam. I will upload a video during the weekend, it’s more a rattling than a banging, the pipe is going through the joists so I think it’s hitting them. my other option is to remove the floorboard and wrap the pipe in felt in the areas where it hit the joists
    – Antonio MG
    Feb 5, 2020 at 19:41

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