Thanks for all these ideas. The annoying thing is if I go downstairs right now and turn on power to the unit it will start right up and run fine until everything is up to temp. It's only the next time it tries to turn on that it wont fire up. It just tries over and over.
Bigdog, I know that this water heater isn't as efficient as a real boiler. I'm just heating a 450 sf basement shop to about 50 degrees. If I have a big project going I might turn it up to 55 for a couple of days. I just didn't think I needed to spend 3 or 4 thousand dollars for a real boiler for this application. The whole thing has worked fine for over a decade.
So what I've been doing the last few weeks is to just turn it on and let the floor/room heat up then turn it off when I hear it failing to light. I will find time soon to go over the manual.