The faucets in my parents’ house are extremely sensitive, having a very narrow band of acceptable temperatures.  I’ve asked several plumbers and two of them have come to the house, but so far none of them have come up with a solution.  The details…

Every faucet in the house behaves like this:

1. Adjusting the temperature of the water heater simply moves the location of the acceptable range, but not its width.
2. This happens on every faucet in the house, ranging from 2 – 30 years old, with at least 3 different brands.
3. The same thing happens on faucets with separate cold/hot knobs… both the cold and hot adjustments are hyper-sensitive.