Patent ID: 8876524

Claim:
A method of operating a combustion appliance that has a burner, a variable speed combustion blower, three or more different firing rates including a minimum firing rate, a maximum firing rate and at least one intermediate firing rate between the minimum firing rate and the maximum firing rate, wherein each of the three or more firing rates have a different corresponding combustion blower speed, the combustion appliance further including a first pressure switch and a second pressure switch, the combustion appliance operating in a number of HVAC cycles in response to one or more calls for heat, the method comprising: receiving a current call for heat to initiate a current HVAC cycle; setting the combustion appliance to a first firing rate, wherein the first firing rate is above the minimum firing rate; igniting the burner of the combustion appliance; once ignited, modulating the firing rate from the first firing rate down towards the minimum firing rate; determining if flame is lost as the firing rate is modulated down towards the minimum firing rate or after the firing rate has been modulated down toward the minimum firing rate, and wherein if flame is lost: setting the combustion appliance to a second firing rate, wherein the second firing rate is above the firing rate at which the flame was lost; igniting the burner of the combustion appliance; maintaining the combustion appliance at a third firing rate that is above the firing rate at which the flame was lost until the current call for heat is satisfied or substantially satisfied; and initiating a calibration cycle subsequent to the current HVAC cycle to identify an updated minimum firing rate, the calibration cycle comprising changing the blower speed of the variable speed combustion blower until the first pressure switch changes state, determining a first blower speed that is related to when the first pressure switch changes state, the first blower speed corresponding to the updated minimum firing rate of the combustion appliance, changing the blower speed of the variable speed combustion blower until the second pressure switch changes state, and determining a second blower speed that is related to when the second pressure switch changes state, the second blower speed corresponding to an updated maximum firing rate of the combustion appliance.