Carbon Monoxide is a silent killer: it has no colour, taste or smell. Even low levels of Carbon Monoxide can lead to permanent ill-health or death, especially in children. The early symptoms of Carbon Monoxide poisoning can easily be mistaken for 'flu. They include nausea, headaches, tiredness, dizziness and pains in the stomach or chest. Look out for sooting or staining around your appliance: it is a sign of inadequate venting of gases.