Boiler water is treated to prevent scaling, corrosion, foaming, and priming. Treatment is courtesy of chemicals which are put into boiler water through the chemical feed tank, to keep the water within chemical range.

Oil mixed with boiler feed water can cause a catastrophic loss of the boiler. Even small amounts of oil can lead to foaming, priming, corrosion and uneven heating of the boiler tubes. 

Therefore it is critical to monitor the boiler feed water to ensure there is never any oil content present within the system.