Flashing steam in hot water loop

Equ13

I have a hot water loop off my steam boiler that is very noisy. I’m guessing it is flashing steam based on reading Dan’s books, but it shouldn’t be. It’s a straight bypass install – no heat exchanger – looks identical to Dan’s recommendation on this site. The water leaving the boiler is about 180 – never higher, but the loop is loud, and gets much worse when the circulator shuts off. I have recalibrated the thermometer twice so I pretty sure my temp reading is accurate.

My installer said he s pretty much out of ideas, but that he has never had this problem in any of the other houses he has put this in.

A few clues/ideas I had about this
1) The system is very dirty – it’s a very old large house I recently purchased with single-pipe steam that was poorly maintained and seems to have no end of gunk in the pipes. I’ve been doing my best to skim it which has helped, but the problem is still quite bad.
2) Pressure is too high – the system is set a 2 psig which I know now is too high, could that be forcing steam into the loop?
3) The water is traveling up to the 3rd floor – not over the 30 ft limit, but very close too it.

Any ideas about how to solve the problem would be greatly appreciated.