I have a rheem cretertion II and there are 3 green lights and it will not light but one green light blinks 3 times

Check the flame sensor is clean and the connection is good

Seven (7) blinks every three (3) seconds
Combination Gas Control failure Contact a qualified service technician.

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

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

Rheem does not post service manuals
Gene

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

62-24084-02 LED CODES
POWER LED - GREEN
ON - Normal
OFF - No power to board
OK LED - GREEN
One Blink - One hour retry delay
Two Blinks - Pressure switch failure (remains open)
Three Blinks - Limit switch fault
Four Blinks - Pressure switch failure (remains closed)
Five Blinks - Twinning fault
FLAME LED - YELLOW
ON - Good flame
Rapid Blink - Flame present with gas valve de-energizing
Slow Blink - Marginal flame

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

how many times does the light blink? this is a code

1/ overheat stat 2/ fan 3/ diaphrapm valve 4/micro switch when checking fan be sure to check the very small rubberor nylon hose for pinhole best of luck

Roscoe007 shouldnt speak unless he knows what he is talking about, as a heater installer i am telling you the ignitor needs to be replaced, the very fact that the ignitor does light for about 30 sec than goes out rules out any issue with the themostat, replace the ignitor!

i have a rdgd-075auer series that I am looking for the manual or blueprint to install the board on it.

have service completed