From time to time, when I get up to shower in the morning the water
doesn't get as hot as it should. I can turn it all the way to hot but
it's still not as hot as I'd like it. On most days, I'd get scalded
shortly after turning it all the way to hot. I used to think this was
because of our water heater, but I just replaced that a couple of days
ago because it sprung a leak. Is the next likely culprit the mixing
valve in the shower? Could it be corroded or gunked up or something? I
know nothing about them but I can't think of anything else that could
cause this problem.

Thanks,
John