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thermostatic vs. pressure balance
(Chris Lewis) writes:
Another question I had was that if the thermostatic valve is
supposed to produce a fixed temperature output, what does it do when
the target temperature is impossible to obtain with the input water
supply? For example, if I demand 110 degree water but my hot water
pipe is full of 65 degree water, what happens? I was told by another
salesperson that the thermostatic valve merely sets a maximum possible
temperature. But if that's true, then when someone turns on the hot
nearby, or if the washing machine gets turned on, then it seems like
I'd get hit by a sudden blast of cold water. Is this true?
If the valve can't make it, it can't make it ;-)
Obviously something has to give if there's no hot water.
Some of the thermostatic units may have a "shut the water completely
off if I can't make the setpoint" feature. You'll have to read the
instructions carefully or call the manufacturer to find out for sure.
Most major valve manufacturers (eg: Moen) have support lines just for
questions like this.
I'll give this a shot. The notion of being able to call up and
actually talk to someone with a clue seems sort of novel; it didn't
occur to me that it was a possibility.
Pressure-balance valves can't have such a feature because they don't
know what the water temperature is.
I think I have a decent understanding of what pressure balance valves
do, just not how they do it.
[Which is sort of unfortunate, because now we have a teenager that's
difficult to get out of the shower ... Instead of cracking open
a nearby hot valve to get him out, I have to go down stairs and shut off
_all_ the water, and he whines about being still covered with soap ;-)]
Hmmm. Maybe I should install a special shutoff on the hot to prepare
for this possibility in the future. 
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