Abstract: A device for augmenting the control of a forced air furnace includes a heat probe which is located in association with a furnace heat exchanger so as to sense the air temperature of air passing across the heat exchanger. The probe is connected via a buffer to an optical controlled switch. A latch is associated with both the probe and the switch such that in response to a high temperature turn off point the optical coupled switch shuts off the furnace solenoid associated with the furnace and maintains the solenoid in an off position until the probe senses a low temperature turn on point. Upon sensing the low temperature turn on point the solenoid is turned back on and is maintained in the on position by the latch until the high temperature point is again reached.