I've recently installed solar hot water and as expected it gets extremely hot. I would like to keep the tank as hot as possible (>180°F) and simply mix down the water to 120°F / 50°C as it's used so the tanks charge lasts longer. The sun doesn't always cooperate however and it can obviously get much colder than that.
The solar company installed a thermostatic mixing valve, however it doesn't hold the temperature at 120°F. Depending on how hot the tank is (120°F - >180°F) the temperature at the faucet fluctuates greatly.
Is there a valve that will simply keep the temperature at 120°F no matter what the source tanks temperature is? While it is at least >120°F of course.