RTG-74PVN was working perfectly and after aproximetly one year+ stops ignating. We used pressure air to clean inside but didn't help. Looks reely clean inside, like new but fails to ignite four of five times. I can't see any of my gas pressure change on my stove in the kitchen. John

Imperfect Combustion
Clean air inlet filter.
Clean combustion air fan.
Clean heat exchanger fins.
Check for adequate combustion air ventilation openings and clean if necessary.
Check vent system for partial blockage and correct as necessary.

check the air intake

Before calling service technician, open following links for resources including Rheem chat and possible manual:
http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html
http://waterheatertimer.org/pdf/No-Error-Code.pdf
http://waterheatertimer.org/Crossover.html

Typical tankless manual says to have yearly service which includes checking household plumbing, gas supply, vent and condensation, check sensors for loose wires, clean and inspect burner parts and ignition factors etc.

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.

I'm not an expert but I used canned air and blew out the inside of my heater and cleaned my air and water filters..

I've had my water heater for 2.5 years and this is the first time I've had any problems. So far, things seem to be working okay.

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.

its a code for the oxygen sensor, first step would be to ohm it out see if it is working right, then i would go after make up air in the room, cleaning it will only help if the sensor is clogged

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

I had the same problem with my Paloma a year and a half after installation...contacted Rheem customer service (800-432-8373) and they recommened a local installer in my area. The technican diagnosed the problem as the "flow control valve"; he managed to get Rheem/Paloma to cover the part under warranty...I only had to shell out the money for the install.

It is normal problem because u r heater is so old
out of company warranty so open it and clean it

NOTE

dont touch it after use means open it before use

means when it is not use in 1 hours because heater contain power in one hour after use