Replace High Limit Aquastat?

I have a Burnham Series 2 50K boiler heating the first floor apartment in my house. It's about 7 y.o. Tenants have complained that the heat was slow to come up since the day it was installed, but the installer came back to check and ensured that everything work working as expected. While working on another boiler in the basement I recently decided to give the Burnham system a checkout and discovered that the boiler shut off (during a heat call) at a supply temp of about 145 deg., as measured by my clamp-on thermometer about 2 feet from the boiler, and cycled back on at around 125 deg. These numbers were roughly similar to the boilers internal themo/pressure gauge numbers.

This boiler doesn't have any low limit wiring, etc, so it just has a high limit aquastat. It was set to 180 deg. per its dial. I bumped the high limit up gradually and now have it set at about 210 deg to achieve a measured max supply temp of 180 deg. My question is, is this dial just badly mis-calibrated, or is the high limit aquastat broken and should be replaced? I measured the output over several boiler cycles and it seems to shut off consistently at ~180 deg. now.

The heat it working much, much better, recovering from overnight setback in less than an hour, when it was taking 2.5 hours.