Time-delay for automatic reset of furnace

Abstract

Automatic reset for an unattended gas furnace has an induced draft blower motor energized by an electrical power source and with a first, normally 'open', relay switch in circuit to control the operation of the blower motor. A burner control circuit, energized by a transformer coupled portion of the power source, has a room thermostatic switch, a second, normally 'open', relay switch in series with the thermostatic switch and an air-flow switch operated by airflow in the furnace to connect the control circuit to the second power source when the blower is 'on' and the thermostat is 'closed', calling for heat. The second switch is connected to the control electrode of an electronic switching element to energize selectively a relay controller which, when energized, closes both the first and second relay switches to energize the blower motor and burner control circuit. A timer, having a predetermined time interval, is connected to energize a second electronic switching element connected to shunt energy from the first electronic switching element to deenergize the relay controller after elapse of the time interval to enable the two relay switches to 'open', thereby cutting 'off' the blower and burner to automatically reset the furnace from a lockout condition.