I think you guys nailed it...

Unknown

We talked about it here recently, it takes too long to heat up and cools down too quickly. Per the suggestions here I looked at it again yesterday. I'd say the piping is only ~ 50% insulated and most of what's missing is closest to the boiler. It's "always been like that" because nobody remembers anybody removing it and they've been in that house for 40 years now. It wasn't a problem until they removed the big mass boiler and put in the low mass one. The sad part is, so many men from so many different companies came out and have looked at this, all with their own theories of how to fix it. Not ONE caught the insulation problem and identified it as a possible source of the problem. I'll insulate it come fall if they are still there and let you all know how it worked out once the cold weather comes back. But in the meantime, thanks! :)