Bosch WR18G Geyser not heating water enough. It worked fine last winter. What could cause this?

SOURCE: Tankless water heater pilot light will not stay on

It is most likely the water valve stuck open, telling the controls to heat water, that it thinks is flowing through it, but without actual flow it overheats. Depending on how comfortable you are with taking it apart yourself, you could open the valve to see if it just needs cleaned out, or if you have a ruptured diaphragm or some other cause.

SOURCE: Whirlpool Energy Smart water heater not hot

I think some one mis informed you, the normal temp on any water heater from the factory is 120, it should not go above that for reasons of sevear burns, as far as it't smart part it's just a name, you will lose a couple of degrees just comming torm the tank to the faucets, the water heater will allways keep the temp in the tank at what ever it is set at, it doesn't have the brains or computer to know what time of day it is but when the cold water comes in to the tank it comes thru a dip tube that goes to aprox 1 inch from the bottom of the tank, if you take a long shower and do not have a energy efficant shower head you can use up to 5 gals, per min of hot water where an energy efficant one only uses 2.5 or less and still has the same pressure at the shower head, the temp in your water heater tries to stay at the setting it is at depending on how much is used at one time meaning washing machine, filling tub or dishwasher at the same time, it lets more cold in as the hot goes out and as you know it can only heat up so much at a time and the cold water is just going across the bottom of the tank, so the name is just that no diffrent then any other water heater unless you went to a tankless water heater.

SOURCE: warm water only

You can eliminate the shower control knob possibility by turning on your hot water anywhere else in the house. If you get hot water in other places, then it could be the knob causing it. A substantial lime buildup in the tank can also cause poor heat transfer from the elements to the water.

SOURCE: richman gas lp tankless hot water heater. used for

I had the same problem with my Paloma a year and a half after installation...contacted Rheem\Paloma\Richman customer service (800-432-8373) and they recommened a local installer in my area. The technican diagnosed the problem as the "flow control valve"; he managed to get Rheem/Paloma to cover the part under warranty...I only had to shell out the money for the install.

SOURCE: Instant hot water dispenser does not heat water.

I had the exact same problem. I even replaced the first unit with a second unit...because I was sure I hooked everything up correctly. Then I called their support line and and felt very stupid. They asked one question "are you plugging in the Quick&Hot into the same electrical outlet as the garbage disposal"?. I said yes..and the garbage disposal works fine (thinking that this indicates a good electrical outlet). She then said "That outlet works off of a switch so no electricity is getting to the Quick&Hot until the disposal is turned on). Gosh darn it...that made total sense. I then tested this out by plugging an extension cord into a different outlet and it worked fine. Boy...do I feel stupid. Hope this helps.