pulsing hot water at low flow from faucet

[Anthony Evans]

I have a shower/bath that if you turn the hot water on and get a reasonable flow, as the water warms up the flow diminishes. If it diminishes below a certain point, the water stops. If the water is flowing a bit stronger so it doesn’t stop, it starts pulsing with a knocking sound. If the water is flowing faster there is no pulsing or knocking. I have replaced the washer countless times. It is the only faucet in the house that acts this way.
Two things: why does the hot water diminish so greatly when it heats up (again, only with this faucet) and how can I stop the pulsing & knocking ?

[CincinnatiPlumbingParticipant]

It could be a few things. Without seeing it firsthand its hard to tell. Since you’ve replaced the washer I’m assuming its stems/seats and not cartridge. My first guess would be the washer though. As the water heats the washer expands. Your washer may be loose or perhaps even the seat. I’d replace the entire stem and seat and see if that solves the problem. I’m not a big fan of just replacing a washer. The stems and seats arent too expensive and you’ve got to take the stem out to put the new washer on anyway. Might as well go with all new parts if you’ve gone that far.

[Retired plbg1Participant]

He is right usualy the washer swells up if water is to hot, so when you get new stem rell guy about your problem maybe he can put in washerthat does not swell. Let us know, I know they use to have some washers for hW they were a little harder.

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Art retired plbg

[PlumbingInspectorParticipant]

Try a flat washer instead of a beveled washer it won’t swell as much.

[CincinnatiPlumbingParticipant]

Just a reply to John who posted his reply to this post in the guestbook rather than here. John, I recommended replacing the stems and the seats. Along with the stem would come a new bib screw.

[thosmParticipant]

Well, all you water wizards and wonders, This is what happened:
Thinking stems and valves, I went to the bath and looked at the wall. Not easy to replace plumbing behind tiled walls when the other side is also sheet rock. I needed another answer.
I am running the hot water a little on the hot side (180+). So wondered at the softness and flexibility of the present day ubiquitous black washers. I went down to my stash of old washers and found a flat red, fairly hard washer and installed it.
Haven’t had any problem since. No banging, no losing the hot water when it gets hot. Is this red washer something that has gone out of style?

Thanks anyhow for your input.

[CincinnatiPlumbingParticipant]

Wow! 180 degrees huh? That is WAAAAYYYYYY hot! In fact the only time I’ve ever seen water that hot from a water heater is for restaurant use. I never set water heaters higher than 120 degrees when I install them due to burn issues. 120 degree water can cause burns, but one would have to be exposed to the water for 15 seconds before it happened. 140 degree water causes serious burns requiring hospitalization within 3 seconds. I can only guess how fast one could get a serious 2nd or 3rd degree burn from 180 degree water.

I worked with a guy about 2 years ago who was working on a heating loop. He had frozen the line, but due to the water being 165 degrees the ice dam broke loose and caused 3rd degree burns over 30% of his body. He was in the burn unit for about 2 months and off work for an additional 4 months.

The washer you’re asking about is available from most plumbing supply houses.

[CincinnatiPlumbingParticipant]

Just found a webpage concerning the time it takes for water of varying temperatures to cause burns. According to the chart, 180 degree F water will cause an instant burn.

Hot Water Burn and Scalding Graph

[thosmParticipant]

I’m not sure about the temp. That’s what the reading is on the furnace boiler. I didn’t set it, the furnace repair man did. The water is hot, but it builds the heat more than slowly enough to avoid a real burn.

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