Im a hvac tech new to hydronic systems was doing a heating inspection on a 1950s bryant copper tube boiler closed loop system with 2 zones not sure how control works no information at homeowners.It was set for 90 degrees and had a senseing bulb going outdoors and another senseing bulb going inside boiler cabinet I believe on one of the copper tube supply at top of boiler.not sure what they are trying to control?a constant loop temp. of 90 degrees? Would appriciate any help.Thanks