There are several factors which could lead to this. Depending on what the weather is, your hot water may be cooling off faster in the pipes before it gets to that specific location. If the pipes are in an outside wall they could be cooler, as well. I find that we need to make a seasonal adjustment in the temp of the water heater to keep the water temp in the shower comfortable. In other words, it might not be your faucet.

Helene

The best thing to do is take an accurate temperature reading with an instant read thermometer (the kind you use for cooking). Do it when the hot water hasn't been used anywhere in the house for several hours. Hold the thermometer under the running water. Take the temperature when you first turn it on (after it gets hot), and then again after 1 minute, 2 minutes, 3 minutes--you want to see if the temperature drops off rapidly. Also take the temperature in a sink faucet. Personal perception is very subjective, and what feels cold in a shower could feel very warm to wash your hands with in a lav sink. You want to see if you have consistent readings throughout the house because it could be a problem with the water heater. Shower valves now have temperature limit stops, which you can change. Water that felt plenty hot in the summer will now need to be turned hotter (assuming you live in a cold climate) to "feel" the same. Report back with your findings and we'll take it from there.

Both are helpful responses. Thank you!

I can take temps throughout the house but the shower in question is on the same outside wall as the other shower in which I haven't experienced the problem (and both are pretty much the same distance from the water heater). The sink furthest from the water heater has NO problem (although as suggested, hands are not as sensitive as whole nude bodies!). Also, I'm talking a HUGE change in setting even comparing from last winter which was much much much colder than this year to date. I used to rotate the knob 45 degrees toward full hot and now am rotating 180 degrees (full hot is at about 270 degrees rotation).

If there have been no changes to the water system in the house...no valves opened or closed, etc, no additional work done...no one futzing with the water heater...it leads towards the valve itself. Still, I'd check any gate or ball valve on the branch line and make sure they are full open.

Could be debris in the pipes that made it into the shower valve and are limiting it's movement. Debris could be from anywhere....gunk from the hot water heater, bits of solder that let go, to basic grit from well water that made it to the valve. Perhaps work out by the street stirred up sediment in the city water.

As an aside, if you have the shower temp set to a comfortable temp and flush a toilet, or (more stressful on the system) simultaneously flush a toilet AND turn on the cold water at the sink tap, how does the shower react over the following 60 seconds? Does the shower water volume change? And/or does the water temp change? Or does it not miss a beat at all?

Your valve probably does not have stops, but if it did, it'd be worth checking that...though how the stop got rotated would be a head-scratcher.

Can you turn the valve to cold and check the water volume flow. Then turn the valve to full hot and check the volume flow.

It could be the water supply, debris in the system, the anti-scald feature being off a bit, etc.

Some valve have a set screw that limits temp by limiting the rotation of the handle. You don't seem to have rotation problems, just temp problems.

If you know what kind of valve you have, you can normally get a pdf file from online that shows you how to take the face plate off the valve, then remove the cartridge, flush the system, then reset everything. It's usually a good time to replace the existing o-rings with new ones. For common valve, maintenance/repair kits are readily available and only cost a few dollars. Or the cartridge itself may need replacing.

Vague answers, because...."it depends". lol

It depends on your valve, but household tools can usually do the job.

mongoct - Your answers aren't vague; you just gave me plenty of options! When I got home I checked the brand faucet and pulled up FAQs for the model on the mfr site. Sounds like my condition could be due to deposits on the pressure balance valve. Seems like a trip to the friendly local hardware store is in my future. Thanks!