Please help understanding Thermostatic Mixing valve

[Ron Takeda]

With a Thermostatic mixing valve; is the cold valve completely shut off until the hot water becomes too hot? I've had a Grohe Thermostatic mixing valve in my shower for years and I love it. However I always question if I"m wasting water (cold side) while I'm waiting for the hot water to arrive.
I"m building a new shower and would like to get another Thermostatic mixing valve - but only if it's not going to waste water.
Can someone tell me if Thermostatic mixing valves only turn on the hot side until cold water is needed?
If both cold and hot water are turned on immediately I will get a regular pressure balance valve where I'm in control of turning on only the hot water until I need to mix in cold.
Thanks in advance.
Ron

 

[Sylvan]

I happen to like Delta pressure or temperature balence type

Normally you place the valve to the upper most hot water which should have been adjusted to limit the HW to 120 F MAX

As the water starts to get hotter then you start adjusting it to the temperature you are comfortable with

Or you can just set the temperature setting to your liking and just leave it there and wait a minute or so. Hopefully you do have return circulation on your HW