My tankless has been working fine for the past 5 years, until 2 nights ago we had no hot water (error code 12). So I reset the system and this morning I had no hot water... again it read error code 12 again!!! So I decided to do some research and found this great forum.
BTW I have city water.
Based on the info I got on this forum I turned the power off, cleaned the air mesh/filter, I also removed both flame sensors and cleaned them with a scouring pad; however as I was removing the sensors there was a a fiber-glass like gasket that disintegrated in my hand (so I guess I need to order one) the other issue and BIGGEST CONCERN is that there is a hole about a 1/2 inch wide, on the left side of the sensor that now has a fairly decent FLAME COMING OUT OF IT every time the heater is in use!!!