A gas outlet monitoring system for a boiler system includes a gas probe(s) with a plurality of gas sensing locations wherein each location measures a plurality of parameters of the gas flow, such a oxygen concentration and temperature. The multi-sensor probe includes a tubular lance and a plurality of sensor pods spaced along the lance. Each sensor pod has an oxygen sensor disposed in a first port, and a first temperature sensor disposed in a second port. An enclosure is disposed at one end of the tubular lance. The enclosure has a respective pressure sensor for each oxygen sensor port. A plurality of first tubes passes through the lance between the enclosure and the first port of a respective sensor pod to provide a gas to the respective first port for the purpose of providing cleaning air. A plurality of second tubes passes through the lance between the enclosure and the first port of a respective sensor pod to provide fluid communication between gas in the respective first port and the respective pressure sensor. One pressure sensor is provided for each oxygen sensor.