Schematic view of heat system. Zone pumps are controlled by a thermostat. Front heat is controlled from driver control panel. Blower motors have a manual switch with a thermal switch so the blower won’t come on when the water temp is below 104°F. Heat exchanger provides both heat and domestic hot water while engine is running. It will also heat the engine from the boiler for cold weather engine starts. Domestic water is 120VAC or gets heat from the boiler.