No green light on, power gets to unit but no light or red light and no hot water. Thanx. Rob

Not sure about modern heaters with lots of lights but inside there is usually a pressure switch that prevents operation if the water pressure falls and a temperature switch that cuts the power if the temperature rises too high - in a single heat unit there are only two wires supplying the heater element and the temperature is controlled by the water flow. It is straightforward to use an ohmmeter to check the element but with a multi-heat unit there is likely to be a switch to contend with and several connections to the heating element.
In this case it is a good idea to draw out the circuit so it makes more sense - if the element tests ok, it is likely one or the other of the safety switches is faulty.

While it could be many things that have gone wrong, the most likely cause is the heating element has failed. Call the local dealer.

You might have crossover problem caused by bad faucet cartridge.
http://waterheatertimer.org/Crossover.html

The green standby light should come on when 240Volt power is applied. Page 6 manual.
Both red lights should come on when tankless is activated. Page 6 manual

RTE 13 requires 60 amp breaker and 6 gauge wire
http://waterheatertimer.org/How-to-wire-Tankless-electric-water-heater.html
http://waterheatertimer.org/pdf/Rheem-TanklessElectricUC_AP15447.pdf

Factory temperature setting is usually default 120 degrees.
Adjust temps page 11 manual
Thermostat calibration is always approximate.
120 degrees is not hot enough to burn the skin.
Exceptionally cold incoming water temperature can cause tankless not to heat enough hot water: install tempering tank to preheat water to room temperature.
Tankless cannot be exposed to more than 11 grains hardness in water. Delime tankless yearly, clean water filter monthly, do not install low-flow restrictions or conserve water since the flow rate must remain high for tankless to activate.
Rheem does not post service manuals for their tankless water heaters.
Call Rheem 800 432-8373

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Hi, The thermostat on most hot water heaters is part of the gas control unit.
if you disconnect the wiring on an electric unit or the piping on a gas unit the whole controller should screw out. Make sure that the electrical power is off, gas **** is closed and water tank is empty.
Hope this helps.
Rob

This will be a thermostat or element problem. The red light tells us that you have power to the unit. If you are handy you can test the thermostat and the element with a continuity tester. A voltmeter may also be used. This will tell you where the fault lies.

Your 220v hot water heater does not need the neutral(white) wire coming in. Bare wire goes to ground -green headed screw. Black goes to black, Red goes to red. White gets teminated with a wirenut or some electrical tape.

Try this first before condeming the unit.

1. Turn off the power supply to the Digistat SCR (receiver unit)
and leave for 5 seconds.
2. Turn on power to SCR unit and check red light is on.
3. Press override button No.2 and check the green light comes
on and boiler fires.
4. Press & hold down button No.1 (Keep depressed), then
press No.2 and keep depressed. {The Red LED light will flash
a couple of times and then it will go out}
5. Now release both the buttons – {the two LED lights should
come back on}
6. Get the Digistat+2RF/+3RF unit and stand two metres away
from the SCR unit with the Digistat+2RF/+3RF unit in your hand.
7. Remove the battery cover and fit the batteries.
8. The Red LED light on the SCR will now flash for approx. 7
seconds.
9. This confirms that the radio signal is being sent and
received.
10. The Digistat+2RF/+3RF and the SCR are now successfully
linked by a dedicated RF address.

Take the cover off and look for reset that has trip.If you can't find no reset turn the power off and wait for five minutes,turn on and turn water on also to see if you get hot water.