Cleaned and checked gas boiler. Checked voltage & amp draw of pump. Inspected heat exchanger & flue venting. cleaned burners & pilot assembly. Found expansion tank water logged. I drained expansion tank. Tested boiler operation with combustion analyzer. CO: 200+. Fine tuned for proper burn. Adjusted combustion air door. Adjusted gas pressure: 2.85 inches. Carbon monoxide: 85 ppm. Oxygen: 5.1%. Stack: 530. Rate: 219,000 BTU.