Preform furnace cleaning and replace 413 filter. Clean out drain and all pressure tubes wipe down entire unit inside and out. Heat exchanger is good prefom combustion test. No co found in the air stream. System is operating safely at this time install water and freeze protector on sump pit. Helped customer hook up to there phone. The corrosion on the fitting is normal. Boiler system has antifreeze in it. Thanks Brad If any problems come up with the sensor let us know If you could take a few mins and fill out a survey on how I did that would be greatly appreciated