Contaminants come from only two sources: the fuel or the combustion air. Potential fuel contamination should be investigated, especially with fuel oil and LP gasses, but natural-gas supplies can occasionally be affected as well. “Bad” fuel will contain higher than acceptable levels of sulphur and other contaminants. Modern standards are intended to ensure purity of the fuel supply, but off-spec fuel can still find its way to boiler rooms. It is difficult to monitor and analyze the fuel itself,
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