When turn on the hot water only the top red and green lights are on and the water is not hot

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

Clog in hot water line?

Replace heat trap nipple at top of water heater?

http://waterheatertimer.org/Low-hot-water-pressure.html

http://waterheatertimer.org/Whirlpool-Energy-Smart-electric.html

http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html#intellivent

http://waterheatertimer.org/New-water-heater-making-noise.html



Gene

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

Call whirlpool / they will ask for serial number
http://waterheatertimer.org/Whirlpool-Energy-Smart-electric.html#part

Gene

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

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

you need to shut off the the red nob and turn the nob off in front take the cover off remove the heat shield turn the nob on top to pilot use a piece of paper to light put in next to pilot and hold button down for 20 to 50 secs pilot should stay lit turn nob on front then burner should kick on then you should be all good

did you dry fire it and burn out the fuse?

It may be bad thermostat terminals of the water heater, or, alternatively, the very top heating element is in need of replacement. See this handy diagnostic article for more info:
http://yourhandymanzone.com/Your_Handyman_Zone_How_To_Pages_Home_Improvement_Zone_Heating_Systems_Water_Heaters_Cold_Water_Still_Released_Despite_Water_Heater.htm

Hope this helps.
Brad