Abstract: A fault detection system and method for a warm air furnace is provided. A sensing circuit connected to an AC power source measures a level of current consumption during several points in the warm air furnace operating sequence. The measured level of current consumption is compared with an expected value. If the measured level exceeds the expected level by a threshold amount, a fault in the warm air furnace may be detected. An indication of at least one warm air furnace component that is most likely to have caused the fault may be provided.

Abstract: A solid-state fail safe gas valve system in which first and second gas valves are arranged in series in a gas passageway, the valves being actuatable by first and second solenoid operators respectively, the second operator requiring a voltage greater than the operating voltage supplied to the valve system to achieve actuation. The operators are separately energized through microprocessor controlled switches so that a capacitor connected across the second operator and its switch is pumped to a voltage above the supplied voltage by voltage induced by interrupted energization of the first operator.

Abstract: An ignition circuit and method for a hot surface ignitor. The ignition process and apparatus enforces a short warm-up period for the hot surface ignitor where approximately half power is supplied at start-up to the ignitor until the ignitor warms to a point where its impedance is increased. By warming the ignitor gradually, the system power supply is not pulled down to a level which may cause malfunction of other electronics connected to the same supply. Further, the voltage level to the ignitor is controlled so that service life of the ignitor is extended.