My Rinnai RC98i has been working well since we bought the house 4 months ago. Yesterday we came home late to find that we had no hot water, and every time we turned on the hot water, the Rinnai would beep at us and flash an error code 12, "flame failure". I looked around a little last night and then went to bed. This morning, it still wouldn't work. I verified that my furnace is working, so it seems we are getting gas into the house. I took a look at the Rinnai vent and it appears to be fine. I turned off the Rinnai keypad, turned off the gas to it, unplugged the thing as well, waited 10 minutes, then turned everything on again, but nothing has helped. There is a small glass peephole roughly in the middle of the mechanism (when the cover is off) that I assume is the burner view port (though the manual never seems to identify where the view port is), and there is nothing in there -- it is just black. When I turn the Rinnai on and turn it off, I would have expected to see a spark or something back there, but no, it remains completely black. 1. Am I looking through the burner view port? If not, where is the burner view port? 2. Any idea what might be wrong? Can you think of any other things I could check and give me instructions on how to check them? Thanks!

Water Heaters - Rinnai - RC98i Tankless Water Heater 9.8 GPM 199,000 BTU