My hot water tap: why does it go from pour to piddle?

The plumber for the apartment I live in recently came by to fix my bathroom taps. The seal (or whatever) was worn down so you really had to twist to turn it right off.

Now, it does this thing that one of my mom’s taps does. When you turn on the hot water, it initially comes out in a pour, just like it used to. HOwever, as the water gets hotter, the water flow slows drastically, sometimes almost all the way to “no water at all” depending on how much I turned it in the first place. This means that when I’m getting water to the right temperature, I have to constantly turn up the hot water tap to keep the flow from getting cold.

What is the cause of this phenomenon?

Rubber seats and washers will expand when the hot water comes through, restricitng flow. When turned on initially, the cool water doesn’t have this affect.

As it wears, it will be less of an impact. But still, some flow may be restricted.

Quite normal.

This may be a stupid question, but has this always been normal? I don’t recall in past years a new washer taking it from – here I’ll estimate – a fluid cup of water in a couple of seconds to a cup of water in 20 or 30 seconds. That seems like a drastic drop to me. I’ve only noticed this in relatively recent years, which made me wonder if it was some kind of ridiculous water-saving measure. No?

It is possible that a a restrictor was added, which would add to the problem.

I’ve got a tap that does the same, once I get it running at all. I can live with the slow decline. What really annoys me is turning it on at first and having it go from full (or half) flow to a trickle immediately, often with a bang as the water is cut off suddenly. Anybody have an explanation, and hopefully a fix, for that?

WAG here is that when the repair was being done, the faucet assembly wasn’t flushed. I’ve had to flush out solder blobs, and once found a washer screw head noodling around inside the faucet body.

Cecil knows all: Why does the hot water slow to a trickle after initially blasting out?

My guess is that the plumber put the wrong kind of washer in the faucet. However, I wouldn’t rule out what danceswithcats said. But try getting the right kind of washers first.

I tend to agree that it sounds as though a piece of trash is getting pushed up to the faucet when the water is turned on. FWIW, I’m a plumber.