Greetings All-

This morning a very odd issue started in my shower and I am looking for advise. I have a relatively new bathroom (1-2yrs old) in an older home. This morning when I turn on the shower, there is no hot water, just a strong stream of cold. All other faucets and showers in the house dispense hot water with no apparent changes.

The shower in question is a thermostatic unit from Waterworks. Here are some other interesting tidbits:

When I turn the volume to extremely low (think just above a trickle) it dispenses hot water.
When the volume is increased it blasts cold water. This is interesting because typically when we have the shower on "hot", the water stream is measurably less.
This issue occurs both through the tub spout and showerhead.

Thoughts?

Please tell me that I am not going to have to have a plumber rip out the entire marble tile wall and replace the thermostatic valve.:( Do those components typically fail?

I have an update to this issue:

- I called Waterworks and they said that it sounds like a fauly Thermostatic cartridge - they are sending a replacement part.

-While waiting, I took the thermostatic valve out and removed a bunch of calcium build-up. Now I can get a very hot stream of water out of the shower and tub, but I have to restrict the water flow; however, the flow is strong enough to fill the tub or shower in.

Thoughts?
Could this just be the cartridge?
Shouldn't a thermostatic valve restrict output pressure if necessary?