Thermocouple Completed hearing maintenance on one hot water boiler with two zones removed and clean burners, clean, standing pilot assembly, and replaced thermocouple also cleaned burner tray, tested automatic water fill and automatic damper operations also checked expansion tank turn system on and checked operations check natural gas lines and also checked for carbon monoxide. No detected left system working also flush domestic hot water heater. View visual findings from this job here - https://visionshare.xoi.io/?id=XA-DE27-D1FA9441D3F54EDD826158DC7D5CE6F0