A zirconia oxygen sensor in the stack feeds the combustion controller, which nudges the air damper, fan speed or fuel valve to keep O2 at the setpoint for each firing rate. It corrects for changes in combustion air temperature, humidity, barometric pressure and fuel heating value that would otherwise make a fixed setup run lean or rich. It pays back fastest on large boilers with long run hours.
O2 trim is maxed out adding air, either the sensor's drifting or the fan's losing capacity, check both.
Also heard as
- oxygen trim
- trim control
Related terms
Excess air
Combustion air supplied beyond the exact amount needed to burn all the fuel, expressed as a percentage.
Jackshaft
The shaft and linkage system that lets one motor move a burner's fuel valve and air damper together.
Combustion analysis
Testing a burner's flue gas for oxygen, CO, CO2 and temperature to set it up safely and efficiently.
Dial in
To fine-tune a burner with a combustion analyzer until oxygen, CO and stack temperature land where they belong.