Single Bang and Reduced Flow in Hot Water

[LarryLeveen]

While visiting a friend, I took a shower and noticed a single distinct bang and great reduction in the flow of water from the hot water tap. What might cause this and how is it remedied? Is it causing harm to their plumbing? Thanks.

 

[FullySprinklered]

Loose washer, probably.

 

[Sponsor]

 

[Jadnashua]

Was it momentary, or constant after this happened? Did it just bang once, or does it continue?

In the shower, a sudden drop in cold water pressure can cause the pressure balance spool valve to slow total water flow, and if it stuck in that position, it could continue. WHen working properly, it would move back on its own and in the process try to make the outlet temperature stay fairly constant, but that won't happen if it sticks.

Are all of the other faucets' hot flow 'normal'?

Most modern shower valves no longer have a simple valve seat and washer, but if it's an old one, that can be the source of the problem. WIth one of those, at the 'right' flow rate, it can sound like a jackhammer as the washer slows/stops the flow, then releases, and repeats at sometimes a high rate.

 

[LarryLeveen]

When turning on the hot water to the shower — to let things heat up — it appears to have normal flow for around 30 seconds. Then, the flow drops to a trickle (sometimes accompanied by a single banging noise and not a repeated hammering noise), and one has to really crank it up to get any decent flow from that point on. I haven't been particularly careful to notice other symptoms. I just put the cold water on too as one does to get a decent temperature balance and have to fiddle with it a lot to get good temperature. It's not the water heater — there's lots of really hot water available. I do notice when turning off the shower that the hot water tap needs to be turned MUCH more than in any other shower I've used. Hot water flow in all other taps in the house seem to work properly, even the adjacent sink.

 

[LarryLeveen]

Huh, just stumbled across this video. Listen to what he says about OVERSIZE hot water washers swelling under heat and cutting off flow. Think this is the problem?

Sorry the audio is so bad.

 

[Asktom]

Most likely a loose washer. Usually when that happens it indicates that the seat is rough and needs to be changed along with the washer.