Here is the run down>
Water too cold Neon light on:
1). Water flow is too high-adjusting the water flow as follow; open fully both inlet and outlet shut-off valves at the heater, then turn on fully the highest flowing hot water faucet closest to the outlet connection. Adjust the outlet shut-off valve until the water flow from the hot faucet corresponds to the approximately 3.6gal/min at 105 degree.
2). One of the power supplies is not
on-check the breaker box, there should be three ganged breaker, each corresponds to each of the heater power supply.
3). The power supply voltage has dropped-reset the breaker in the breaker box.
4). Temperature dial is turned too low- temperature adjustment is made using the dial on the bottom edge of the unit. The adjustment is between approximately 95 and 135 degree F. Turning the dial clockwise increase the temperature settings.
5). The inlet water temperature has dropped-readjust the temperature dial.
Attached link is for Bosch hotwater heater
installation. This should give you idea as to what to look for.
The following link is Basch Hotwater
troubleshooting Q&A, this should also give you some help.
Please post back on this thread, If
you still having problem.