So, of course it's Christmas Eve and Toto phone support is closed until Monday. Plumber was out very late last night trying to put fixtures on our bathroom remodel so it would be done...very long story. Don't think he's installed many or any Toto products...another long story. Any help or guidance would be amazing!

Issue 1: No cold water in the shower
For the stand alone shower, we have a thermostatic mixing valve (TSST) that has properly plumbed hot and cold water pipes. A volume control valve turns the shower on and off. Our issue today--water gets nice and hot, but never cold, merely lukewarm. We get very cold water from sinks, tub, etc. Ability to take a cold shower is the reason we purchased this valve combo. Plumber has no idea why this is the case. Ideas? Does the anti-scald limiter limit the amount of cold water too?

Issue 2: Tub spout drains for 30+ seconds after shutoff
We have a stand alone tub with a wall-mounted tub spout and hand shower that is low enough to access from the tub. There is a pressure balancing valve and, above that, a two-way diverter valve that is plumbed to the hand shower and also to the tub. When you transfer the flow from the tub to the hand shower or just turn off the water at the pressure balance valve, water continues to flow from the tub spout in decreasing amounts for well over 30 seconds. Plumber again has no idea why this is the case. Ideas here? Is it simply a "feature" of having the tub spout plumbed from the diverter valve, where gravity just pulls out the water remaining from tub line until gone? Or is it plumbed incorrectly?

Thank you so much for your assistance!

2. It's just gravity draining the water that's remaining in the piping between the diverter and the spout. If you had a way to break the vacuum that's holding the water in the pipe it would completely drain in 2 or 3 seconds, but that's just the way systems such as yours work. There's nothing wrong with it.

1) when you say "nice and hot", what do you mean? it is not supposed to get "nice and hot" but only to 109F to 112F deg. if it is hotter than that then it is a code violation. anyway, that could be your problem ??
i can't speak for TOTO but i can tell you the grohe valves are a PITA to adjust.

Thanks. The hot water on the shower is the correct temperature. It's just when you turn the valve to cold, it doesn't get cold. Haven't measured
The lukewarm temperature yet, but it doesn't feel remote lay "cold"

Are the Grohe valves adjustable for cold as well as hot? Toto instructions leave something to be desired.

as far as i know, all those type valves adjust the same way. you turn the handle until you get a reading of 109-112 on a thermometer held in the water flow . then you set a screw or fix a tab so the handle will not turn further towards hot. now shut off the volume control/s put back the trim and leave the temperature control alone.
the setting of the temperature is a safety thing. they don't want you to get scalded nor do they want you to jump backwards because the water got too cold. it may be by design that it will not get cold? TOTO can answer that question monday after christmas..