Came out today for a Weil-McLain boiler not operating properly. Upon inspection I found that the spill switch was tripped. I reset the switch and the system started right up. I tested the system by calling for heat and it started without any issues. I tested the systems operation by calling for heat multiple times and each time it started without issues. I took a combustion analysis test as a precaution and I received the following readings, 02 is 13.4% and the co levels are 4ppm. The most common reason for this switch to trip is a down draft coming down the chimney. Recommend installing a cap on the chimney. The homeowner stated that he had this issue in the past. The system is operating properly at this time.