If D from BC were a plumber:

I told what to do. Make sure that the restrictor is still in the shower head. That alone will solve most of the problems.

Maybe you should install one of the shower valves that monitors the temperature and adjusts the flow to give the desired temperature?

He's been doing it for years. :(

He would be following in the footsteps of Jesus. Now there's a thought.

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Another options is to just stop taking baths altogether. ...though I'm not sure my clients, friends and family would appreciate that!

There are restrictors that go right in the head fitting before it gets screwed onto the stalk. If it is there, you would see a disc with a smaller than the pipe orifice in it. I think they are 11 GPH I can't imagine that it is 11 gpm!

Interesting.

mpm Inscribed thus:

Its not unknown for debris to build up in the pipe and lodge in a bend to cause varying water pressure and flow.

Someone also mentioned that the water pressure would be the same for both hot and cold supplies. This is not always true. One supply could be from a header tank and the other from the main supply. So they would have different pressures. Also the flow rate would depend upon the size of the smallest pipe in that supply.

I see you don't know plumbing. It is like most practical endevours, laden with Murphy attributes that baffle even the experts.

He does have flow. He is running his shower! If there are constrictions/blockages in the cold water line that are not in the hot line, then he can get problems like that. He starts hot water, it takes all the pressure off the cold line, so it won't flow. If he starts with the cold, it gets its pressure at first, and so keeps the hot at bay. He probably also has a low flow showerhead, which has a constriction built in that creates back-pressure which is blocking the cold from entering the mixing chamber. Been there, done that!

Charlie

Copacetic Inscribed thus:

I disagree. The transfer of heat would take place even if the water were moving in either or both pipes.

Its quite common to lag together both hot and cold pipes for a common run. The idea is that the hot water flow prevents the cold water freezing in its pipe and causing a burst.

Admittedly a much less common occurrence nowadays with the use of plastic pipes.

I've seen _fine_sand_, apparently from the water processing filtration, clog up low-flow shower heads.

On the better-made low-flow shower heads, the dumb-ass thing simply snaps out... on the worse-made, a drill bit does the job ;-)

Cure for low-flow toilets, flush twice... and throw a liberal in with that second flush... helps scour the drains :-) ...Jim Thompson

Archimedes' Lever Inscribed thus:

It probably is in gallons per minute, my shower head is rated 4 GPM. ie it will fill a two gallon bucket in 30 seconds. Though 11 GPM seems an awful lot.

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No need to go that far. Don't turn on the hot water and your hysteresis is fixed. Simple.

I have *never* seen anyone do such a stupid thing, even in Vermont where it does get cold (and there is an overabundance of stupid people - Demonicrats).

Since that's after the mixing valve(s), it shouldn't cause the temperature hysteresis he's seeing. My bet is a trashed valve.

They're "better-made" because the restrictor snaps out? ;-)

You keep liberals around your house?

Nope. Such a blockage as you describe is rare, but any such blockage will only affect flow rate maximum, and NEVER pressure.

The pressure will always rise to the same pressure on the feed side of the blockage.

Figure out how water pressure regulators and gas pressure regulators work. It is not by mere blockage.

You do not understand at all. Once water begins moving, the temperature of the water FEEDING that point in the pipe is the master that defines the temperature of the flow from that point on.

You need to understand how in-line water heaters work.

They burn 1200 watts or more to heat water flowing directly over the radiating heating element.

The coupling between two pipes, even if they were soldered to each other would come nowhere near ANY ability to transfer the thousands of BTUs required to heat the water once in motion.

So, the HOT side would HAVE to be on, at at least a trickle, to maintain its feed water temp. THAT heat would then require several minutes to transfer over to JUST THAT SHORT segment of a pipe full of non moving cold water. If it moves, the job is killed immediately. If they are both moving, the job is killed. If neither is moving, the job is killed by homogenization with each other and ambient air.

Regardless, your contention is about as dubious as it gets.

Even the operation of a simple water cooled PC CPU proves these facts.

If the water is not moving, the cpu only heats the water local to the contact face. Once moving, the system water bath temp takes over... BIG TIME.

Think before you refute. Otherwise you re-size your mouth with your foot.

Archimedes' Lever Inscribed thus:

Agreed ! Bad choice of words.

That is flawed logic, and this is true, even in colder climates, and would ONLY work if the hot side was kept flowing at all times at each endpoint it is carried to.

As soon as flow ceases, the hot begins moving toward the local ambient temp all the way back to the water heater itself.

Basic common sense.