I have a Rheem RTG-74 Indoor LPG Unit. Its about 6 years old, and has worked flawlessly until a few months ago.

1st problem - Water would never get hot on random occassions. Could not reproduce problem at will. Turning water off and back on usually solved issue. No error code seen on display, but no one around read the display while problem was happening.

2nd Problem - a few weeks ago, Error code 13 on display. Would not re-set with simple Water on , Water Off, had to power on and off the main control. Error 13 reappeared next day. Took unit apart. Removed and reset Thermocouple on PCB and vacumned out the burner chamber. Issue has NOT returned.

3rd problem (or maybe same as problem 1). I have now learned to look at the display when water does not get hot, I've observed ERROR CODE 12 multiple times. I have checked main gas pressure at 11+wc. (Since unit functioned in the same spot, unobstructed for 6 years, we can assume venting is all correct).

What is my next step to resolve error 12? Is it the thermocouple that needs to cleaned, or is it the flame rods, or both? Can you describe the cleaning procedure? If cleaning is not an option and I need to replace these parts, can anyone provide the part number and a good source to purchase them at?
Thanks