http://waterheatertimer.org/Troubleshoot-Rheem-Tankless-water-heater.html Tankless Troubleshooting Manual Explanation: Flame Failure. Unit went to main burner for a period of time; but has since lost flame or the ability to verify the presence of flame. At a minimum check the following in all cases: 1. Bleed all air from gas lines. 2. Ensure appliance is properly grounded. 3. Ensure gas line, meter, and regulator are sized properly. 4. Ensure gas type and gas pressure to the machine is correct. 5. Flex lines with a full 3/4 inch inside diameter may also restrict fuel flow enough to give you error code 11. Does the unit have proper inlet gas pressure? No Adjust inlet gas pressure based on fuel type. & 8 ' 9 ( ) , * ' ' + - , . ' : 0 - 1 . 2 / 0 ( 3 1 2 4 ( / 0 3 4 1 2 1 0 6 5 0 2 7 6 0 7 0 0 Yes Unit appears to be OK. Try to restart. Is the burner manifold pressure normal? ! " # ! ! # No Adjust burner manifold pressure. See instructions on page 39. $ " % % Yes Check and inspect burner assembly, flame rods, heat exchanger. 49 ! " # ! ! #