We've recently gone on an "energy efficiency" rampage at the house, replacing bulbs with CFLs, identifying devices that are unnecessarily left on all the time, wrestling with Windows to stay asleep during periods of inactivity, etc. We also recently just installed a "continuous" or "on demand" hot water heater, replacing the 50G direct-vent tank heater we had (it was getting to the end of its lifetime and it was easier to replace it preemptively.)
Unfortunately, the state requires all newly install water heaters to have a thermostatic mixing valve that limits the water temperature to 120 degrees. (For tank systems, it is recommended to keep the tank water at 140, to prevent the bacteria that causes Legionnaire's disease, but 140 is hot enough to scald. But continuous systems have a control system for the output temperature, so can be safely kept at whatever temperature you program in.) And its probably not even working right, since the output temperature is even less than 120. The valve adds cost to the system and to the installation (probably a dozen additional welds in addition to the valve), and while we now have an infinite supply of hot water, generated more efficiently, its not as hot as we like it.
Reputable plumbers are not able to remove or bypass the valve, which means we need to either find a disreputable plumber or I need to do it myself (read: find an incompetent plumber.)
Note to lawmakers: in my many years of successful shower use, I've learned a secret trick to avoid getting scalded: put your hand under the water first -- if its too hot, turn down the water temperature before getting in!
Thanks, elected officials, for making my house systems both more expensive and less useful.