I cleaned my burner unit by watching the video howtolou made on you tube. It took me longermthan his 15 minutes, however after doing everything as instructed I still have the C2 11 code

Two things- Clean the sensor rods or replace(cheap and easy with YouTube instruction video) and at the same time replace the main program chip (also a easy plug in chip). The whole repair takes two hours for a homeowner and costs about 50 bucks for a chip. These are easy an generally the flame sensor rod is the culprit. The code may also be the limit switch but try EZ and cheap first. See You Tube..
https://www.youtube.com/watch?v=npxcVo7RK2c

Multiple error codes can mean PC board failure.
C2 11 is no ignition.
Error 24 is malfunction of operational switch: "press max or mim button on PC board, or replace PC board." On some models, max and mim button can be located just above dip switches, and rotates with screwdriver. See diagram in manual.

Before calling service technician, open following links for troubleshoot resources including error codes, Rheem chat, and possible manual.
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/pdf/ErrorcodeTroubleshooting.pdf

Rheem, Richmond, Ruud, and Paloma are all the same manufacturer. After about 9 months, my tankless RTG-74PVN started giving me error code 11 and cold water!. I fixed it by cleaning the burner, as shown in this video:
www.howtolou.com/clean-a-burner

Before calling service technician, open following link for Rheem error codes and troubleshooting resources:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html

Error code C2 11 is 'no ignition'
Ensure you have gas to the appliance.
Ensure gas type and pressure are correct.
Bleed all air from gas lines.
Ensure gas line, meter, and regulator are sized properly.
Ensure appliance is properly grounded.
Check gas solenoid valves for open or short circuits.
Ensure igniter is operational.
Check igniter wiring harness for damage.

There is no service bulletin covering how to perform these actions.
Rheem will ask that you call qualified service technician, who can give you tips and tricks for keeping the unit working, including opportunity for yearly service that will eliminate the expected $1-8 monthly savings from owning tankless.
Read manual for yearly maintenance needed to keep unit working at prime efficiency.

Rheem, Richmond, Ruud, and Paloma are all the same manufacturer. After about 9 months, my tankless RTG-74PVN started giving me error code 11 and cold water!. I fixed it by cleaning the burner, as shown in this video:
www.howtolou.com/clean-a-burner

Rheem, Richmond, Ruud, and Paloma are all the same manufacturer. After about 9 months, my tankless RTG-74PVN started giving me error code 11 and cold water!. I fixed it by cleaning the burner, as shown in this video:
www.howtolou.com/clean-a-burner -Lou

that error code means not enough gas.
however, there might be something going on with your venting. it could be sucking exhaust air back into the unit. this will cause the same error code.
if your problem is intermittent, then I would suspect the venting to be the issue.

hi pete here ill try and help this could be 2 things check the sensor on the unit the outher one is a qustion has the gas company changed your meter latley and turned off you gas and not come back to light your poilet because this code also means not enough gas or wrong type of gas

11 The Gas Shutoff Valve is not opened
completely.

12 Gas Service has been interrupted.
LP Gas is running low. (LP models only)

I think C7 is where the startup sequence ended...and then you get the error code

If less than a month old...contact your customer support

could be overheat stat or fan check the little hose at the fan area for pinhole next choice diaphrapm valve then micro switch best of luck