We have a plastic/composite tub and shower combination in our master bathroom. Following any use of hot water in the house, including a shower, we will hear a thud or knock noise coming from the tub. It is only a singular thud, repeating every minute or so. Goes on for maybe 10 minutes after the shower ends. Is this fixable without calling a plumber?

 

So you here the noise even if it the hot water use is, say, in the kitchen and not in the bath? Or at least, not in the shower?

If so, then it is likely the noise is called by a pipe expanding when hot and then contracting while cooling and as a result, moving a little and rubbing against pipe straps or a framing member, causing the noise. It may be a simple fix but identifying which pipe is causing the noise may require some detective work, and if the plumbing isn't accessible, say from the basement, may be harder to fix.

If it truly happens with *any* hot water use, then it is likely the main hot water run that comes out of the water heater, so I would start by looking at it. Noise can be caused by pipe straps that are too tight or too loose, so some experimentation may be required. I'd start by getting someone to trigger the noise while someone else listens near the piping from the water heater to try and localize the noise better.

 

Thanks for the response. Yes, the noise even happens, for example, if the dishwasher has just run (1 floor below).

We have had 'pipe hammer' or 'water hammer' in the past, but this sounds different, the pipe hammer was a series of knocks close together but this is a single knock only every minute or so.

We recently got a new water heater and the frequency of this happening went up by a third with the new water heater installed.

 

I agree that it sounds like a pipe expanding/contracting. Your new heater may be set to a higher temperature so hot water use causes it to happen more frequently.

 

Water hammer is not the same as expansion/contraction. Water hammer is caused by moving water suddenly being stopped, by closing a tap say, or washing machine valve closing. Then the energy of the moving water can cause any loose pipes to smack against something, causing a bang or a few bangs.

Expansion/contraction due to heating/cooling is a slower process.