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Yellow flame or soot on a boiler: carbon monoxide risk

Yellow or sooty flame, or soot around the boiler

Address promptly

What is likely happening

A healthy gas flame is mostly blue. A lazy yellow flame or soot can indicate incomplete combustion, which raises the risk of carbon monoxide. Make sure CO detectors are present and working and arrange a combustion inspection right away.

What you can safely check

What an inspector will look at

Does this affect compliance?

Venting and combustion defects are safety items and will be written up at inspection.

When it becomes urgent

If a CO alarm is sounding or anyone feels dizzy or nauseous, leave the building and call 911.

We can help with this

Boiler inspection is something Insparisk does nationwide. To see the local rules for your building, open this in the interactive Problem Solver.

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General guidance only, not a substitute for a licensed inspection or emergency services. For any gas odor, carbon monoxide alarm, fire, or trapped occupant, call 911 first.