I just finished having an Eternal GU145(S) installed. I did the gas piping and had a water heater company install the Eternal. Similar to a previous post I phoned Grand Hall and verified that the Eternal required no annual maintenance other than cleaning the screen that filters the incoming water which is user serviceable, no plumber required. There has been no cold water sandwich problem, though at low flow in the kitchen sink it takes a short amount longer than I think it should to go from warm to hot. This is an extremely minor issue.The default high temperature setting is 140 which is managed by DIP switches on a circuit board inside the cover. I wanted to run a little hotter and it was no problem to change the max temperature after getting the switch settings from Grand Hall. The temperature is changeable in 5 degree steps from the front panel on the unit. There is even an optional remote control available, so if it was desirable to have a hotter (or colder) temperature for a specific job it could be done directly from the remote, I haven't checked on the cost of the remote. I have called Grand Hall 3 times and have never had but the shortest of a wait to talk to a live person. The unit has been running for about 2 weeks and I have been very pleased with its operation.