22% excess oxygen is far higher than normal (typical excess O₂ is 3–6%). This means there is too much air compared to fuel, causing inefficiency.

The corrective action is to increase fuel pressure, which reduces excess oxygen by balancing the air-fuel ratio.

D. Increase the fuel pressure (Correct): Restores optimal combustion balance.

A. Steam atomization: Not relevant unless using certain oil burners.

B. Increase nozzle air pressure: Would worsen the excess O₂ condition.

C. No adjustment necessary: Incorrect because efficiency is compromised.