Hi all, Thanks for reading. My house is heated by steam. In preparation for the winter, we tested the boiler to check whether it's ready. We turned up the temperature, and the boiler fired up. After a couple of minutes, the pressure in the gauge started rising. Once it started rising, it just didn't stop. At some point the safety relief value was triggered and the boiler shut down. Here are pictures of the boiler: I tried to clean the boiler: Emptied the boiler through the cleanout (#4 in the picture), then scraped as far up for any sediment. There was quite a bit - looks like it got hardened. Then unscrewed the vial (#3), then the pressure sensor (#1) and then the pigtail pipe (#2). I turned on the bottom valve right above the bucket in the picture. No water came out. So I shut it back off. I let water run, and it came up through where the glass vial would be. Then I put the vial back in there. I let water run again, and it came up through where the pigtail pipe would screw in. I cleaned up the pigtail pipe so water could go through, then put it back in and screwed the Honeywell pressure sensor back on top. I filled the boiler with water up to 4/5s of the vial. Then fired up the boiler. It took the boiler a while to heat up the water, but then the pressure gauge again went up, crossed the 15PSI, then I shut off the boiler. The pressure gauge kept on going up and crossed the 30PSI, as shown in the picture. The safety relief valve (located on the other side of the boiler) did not go off. But it's not normal (that I can remember) for the boiler to reach anywhere past 10PSI. Any advice on bringing this boiler back to normal operation? Thanks again.