Performed a heating pm on a gas boiler. Removed and cleaned the burner tubes. Checked the flame sensor. Checked the gas pressure. 8.4”wc incoming, 3.5”wc at the manifold. Started and checked the safeties. Performed a combustion test. System is operating properly. 8.6% o2, 4ppm, 82.4% efficient The extrol tank is starting to fail. Water is migrating to the air side of the tank. Recommend replacing.