Control system for gas fired heating apparatus using radiant heat sense

Claim 1

In a control system for a gas fired heating apparatus which includes an inducer, a main burner, two gas valves connected fluidically in series with the main burner and each valve having a controlling electrical winding, and a hot surface igniter for directly igniting gas at the main burner, and which apparatus is adapted to be connected to a thermostat, the improvement comprising: a radiant heat sensing switch having normally-closed contacts which open in response to the igniter being at a temperature above gas ignition temperature and are maintained open thereafter in response to burner flame; a single-pole, double-throw pressure switch responsive to fluid flow effected by the inducer, said pressure switch having a first contact position in the absence of said fluid flow and a second contact position in the presence of said fluid flow; first circuit means including said pressure switch when in said first contact position for effecting energizing of said inducer, for effecting energizing of a hold-in circuit for maintaining said energizing of said inducer independently of said pressure switch, and for preventing energizing of said igniter and the electrical windings of said gas valves; and second circuit means including said hold-in circuit, said pressure switch when in said second contact position, and said radiant heat sensing switch for controlling energizing of said igniter and said electrical windings of said gas valves, said hold-in circuit and said pressure switch when in said second contact position being connected in series.