If the flame on your furnace, boiler or water heater is burning normally, it will be bright blue, with a yellow tip. If incomplete combustion is occurring, the flame will become increasingly yellow. This can lead to the release of dangerous levels of carbon monoxide into the air in your home. Carbon monoxide can be created when combustion is incomplete. Too much fuel or not enough air. It is odorless and can build to lethal levels over time. If you suspect that there is a carbon monoxide problem in your home, do not try to fix it yourself. A plumber can perform a test to determine if carbon monoxide is present. Your unit can then be adjusted or repaired. Symptoms of carbon monoxide poisoning include dizziness, coughing, nausea, headaches, ringing in the ears and spots in front of the eyes. If you believe you are suffering from carbon monoxide poisoning, see a doctor as soon as possible. In an emergency, evacuate the house of all occupants and call for help immediately.