Customer had no heat in home, went to boiler and heard circulator pump running moving water but supply and return pipes cold, found pilot light out, tried to relight pilot and wouldn’t stay lit, removed thermocouple which was very charred and replaced with new thermocouple, pilot stayed lit turned gas valve on and boiler fired, waited until supply and return pipes got hot , had customer feel baseboards in home which were warm, system operational. Boiler is older in age brought this to customer attention.