Help troubleshoot banging pipes

lunchtime33

Hi I am in a prewar building, 10th floor out of 17. There are 2 radiators in my unit. I'm having trouble with 1 of them, where the pipes (I assume it is the supply pipe) makes very loud banging/hammering noises when the heat turns on. It lasts for maybe 30 seconds and then goes away until the next time the heat turns on. It is a 2 pipe system. The plumber has come by and all they did was change the supply valve and the steam trap and checked if the radiator pitch is ok (the radiator itself doesn't seem to make any unusual noises). Changing the trap and valve did not make any difference. The previous tenant actually did not have a radiator here and the supply pipe was just capped. I am not sure if he removed the radiator because the pipes were banging but that seems a reasonable assumption.

Based on what I've found here and elsewhere, it seems this could be water hammer. So I'm guessing I have a supply pipe that is not pitched correctly and water is staying in there. The supply pipe should be higher on the supply valve side and lower where it branches from the riser? The riser is to the left of the radiator.

I'm thinking I can try to see if I can raise the radiator to try to elevate the pipe as well. Does that seem like a reasonable thing to try? Is there anything else I could look into?

Thanks for any advice and suggestions!

Neild5

If you shut the supply valve and the heat kicks on, do you still have hammer? The sound can travel long distances through the pipes.

lunchtime33

With the supply valve closed there's no hammer. There is still some noise but that seems to be coming from the riser and is no where near as loud.

Lance

The fact the valve is closed leaves a cushion of air to absorb a sound wave. Since you say there is still some noise, I would look elsewhere, perhaps a pitch of the pipe near an elbow allow a wave to form and bang? I have heard a sound I was sure was coming from a pipe at one end when it was actually at the other end. Fixed the other end. Done. Good luck.

lunchtime33

Hmm, I can feel the valve move when I hear the noises so it seems like it's coming from fairly close.

Is there anything I should ask the plumber to do the next time they look at it?

delcrossv

The riser to the radiator connects to a horizontal pipe under the floor. That's the likely culprit.

Is it accessible from below?

lunchtime33

Not easily unfortunately. Not without opening up the downstair tenant's ceiling or opening up my floor.

dabrakeman

Without opening something up to evaluate the hidden pipe pitch about the only thing you can do is try raising the entire radiator up a bit maintaining it's correct pitch. Use a 2x4 to slowly and carefully cantilever the radiator up. If it won't budge don't force it. Slide maybe a 1/2"spacer under each leg if you can. Sometimes this will fix the pitch of the pipe below the riser to the radiator.

JohnNY

It sounds like you’re in New York. Tell your building to hire me for a consultation. I help people get rid of the noise in their steam heating systems.