Importance

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Abstract

A control system, for a gas-fired, forced combustion air heating appliance, controls operation of a combustion air blower and a gas valve as a function of signals from a thermostat, a combustion air proving sensor switch, and a gas valve control relay. When the thermostat demands heat, the control system first checks the status of the combustion air sensor switch before starting the combustion air blower. If the combustion air sensor switch indicates that combustion air is being delivered before the combustion air blower has started, the control system immediately halts the ignition sequence. If the combustion air sensor switch is functioning properly, the ignition sequence continues and the control system checks the status of the contacts of the gas valve relay. If the relay contacts which power the gas valve are already closed before the gas valve relay coil is energized, the control system halts the ignition sequence by turning off the combustion air blower, causing the combustion air sensor switch to open and shut off power to the gas valve.

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First Claim