Performed a heating pm on an oil boiler. Brushed and vacuumed. Replaced the oil filter, nozzle and strainer. Started and checked the safeties. Performed a combustion test. 5.2%o2, 4ppm, 0smoke, 83% efficient System is operating properly. When arrived, the pressure relief valve was dripping with the boiler pressure at 20 psi and slowly increasing to 25psi. Checked and found the extrol tank is bad. The is water on the air side of the tank. When the water heats up, there is no place for it to expand. Recommend replacing the #60 extrol tank and pressure relief valve. Drained pressure from boiler and replaced the #60 extrol tank and pressure relief valve. Filled the system and tested. Noticed that the automatic water feed I did not stop and is slowly adding water to the system. Shut the valve next to it. The system is at approximately 15-17 psi. In the future, recommend replacing the autofeed.