I appreciate all opinions and recommendations, both from professionals and DIYers like me. "arcsum68" had the same model boiler and the same problem, so I asked for advice.
If I could afford to hire a professional, I would, but this recession has broken me financially. And if I could afford one, I hope I could trust them.
But when I first moved into this house rental, I had 3 "professional" plumbers look at my boiler: all three had different opinions, but ALL THREE said "I can replace it for $1,000".
If they all said it was the SAME issue causing the problem, I'd have found the $1,000. But they didn't, so I went looking for information to educate myself. All you guys have been helpful enough to educate me about boilers, even more than the "techs" at AO Smith, who can't even give me the right SKU-part numbers, nor consistent information.
Again, you professionals know WAY more than me and "arcsum68", so I'm hoping this discussion will continue in a civil manner.
...at least until my burner stays lit.
RH in CA