I ended up calling Metro Heating and Cooling as it was one of the first I received. Their tech has 10 years experience with boilers and was easy going, calm, explained everything he was doing in a way I understood. And we think he completely resolved the issue.  After a few weeks of the system going out almost every day, I was pretty frantic and frustrated, and so a very calm, confident, communicative tech was exactly what I needed. The other company that had been working on it wasn’t bad, but I think it needed fresh eyes to look at it and see what had been missed previously, trying to diagnose the problem.

Thanks everyone for your suggestions. Thanks for being such a great neighborhood.