Patent ID: 7048537

Claim:
An apparatus for controlling a fuel fired heating appliance having a variable speed blower motor and at least one pressure switch, the apparatus comprising: a first processor for controlling the operation of the heating appliance and for monitoring the opening of at least one pressure switch, the first processor being configured to send a speed request signal when the pressure switch is open for establishing a blower motor speed, and successive speed request signals requesting an incrementally higher blower speed until the at least one pressure switch closes, wherein if the pressure switch does not close within a predetermined time period from the point the pressure switch is first checked after the blower motor has ramped up to speed, the first processor shuts off the fuel fired appliance; a second processor for controlling the operation of the blower motor, the second processor being configured to receive a speed request signal and responsively establish the requested speed for the blower motor, wherein upon request from the first processor the second processor sends a communication signal to the first processor indicating receipt of the speed request signal; and a reset signal monitoring circuit for monitoring the communication signals from the first processor and responsively resetting the second processor when detecting a reset request signal from the first processor, wherein the reset signal monitoring circuit comprises at least one transistor and a non-linear op-amp for comparing the first processor signal voltage at the inverting pin to a reference voltage at the non-inverting pin, and responsively providing an output voltage that gates the transistor to switch voltage to the second processor to reset the second processor.