Soot on gas pool heater burners is a warning, not a nuisance.

Soot on your gas pool heater burners means incomplete combustion, and that’s a carbon monoxide hazard you need to check before using it again.

That black crud is unburned carbon. It happens when the air-to-gas mixture is off, usually because the burners are dirty, the vent is partially blocked, or the gas pressure is wrong. When gas doesn’t burn cleanly, it makes yellow flames instead of blue ones, and that yellow flame leaves soot behind. Left alone, it can plug up the heat exchanger and push carbon monoxide into your pool area or house.

The safety checks are simple: turn the heater off first. Look for a blue flame when it runs—if it’s yellow or lazy, that’s the problem. Check that the vent and combustion air openings aren’t blocked by leaves or debris. Inspect the burner tubes for rust, spider webs, or debris and clean them with a wire brush if needed. But here’s the thing: soot doesn’t usually fix itself with just a visual check. You really want a technician to do a combustion analysis —