So, I have recently had some issues with my boiler (hot water - not steam) system. After hiring some guys to stop by and take a look at it, they told me that the boiler pressure reducing valve, pressure relief valve (stuck partly open) and my pressure gauge are bad (all of which I believe and suspected for some while now). So, effectively I can't leave my auto-feed from the road on because it will over-pressurize the system, and I get water/steam out the pressure relief valve every time it warms up. I did empty the expansion tank after refilling the system the last time (~2 days ago) so I know that it's got somewhere to go if it needs (and it does take on water when the system warms up, but it also comes out the pressure relief valve at the same time).
Additionally, the system was set to ~220F, which they indicated was over water's boiling point and should be brought back to 180, which makes sense and we did so.
However, the system is set to 180F and it's still producing steam and I'm not sure why. We verified that the water is circulating properly and the aquastat is correct as well. The HVAC guy who was here gave me an explanation of why it could still be producing steam even though it's set at 180F but I didn't understand it and after asking him to reiterate it for the third time I gave up. He mentioned something about the backfill of water getting heated but it still didn't make sense to me unless the water wasn't circulating (which we know that it is).
I'd be interested in any explanations - I'm mostly trying to make sure I understand this system. I'm sure I left out some critical details so feel free to comment and I'll add whatever you'd like. This is an old Burnham boiler. Thanks,