Almost 50 people are killed by carbon monoxide poisoning in the UK every year, safety campaigners have warned.
Carbon monoxide leakage cannot be detected by human senses
The Carbon Monoxide Consumer Awareness Alliance, which is launching a drive to highlight dangers, says 42 people died and 177 fell ill in the last 12 months.
It is trying to raise awareness among consumers and doctors as the "silent killer", which cannot be seen, smelt or tasted, can be difficult to diagnose.
The toxic fumes can leak from faulty appliances burning fossil fuels.
Carbon monoxide can be produced when gas, oil, coal or wood is used for heating or to run appliances including boilers and cookers.
Householders are being urged to fit detection alarms and get qualified engineers to make annual checks on appliances.
Symptoms of poisoning can include sickness and headaches.
Lynn Griffiths, president of the CO-Awareness Campaign which supports victims of carbon monoxide poisoning, said people must become "assertive" in combating potential problems.
She said they should look out for symptoms of carbon monoxide, which can resemble general flu-like conditions, food poisoning or a virus.
Ms Griffiths said: "If people in the house are becoming ill, and more of the family are becoming ill, and they're just not getting better, they should go to their GP or A&E department and say 'Could it be carbon monoxide poisoning?'"
The BBC's Angus Crawford said the nature of the effects of carbon monoxide can lead to misdiagnosis.
Some victims have been told they have flu, and sent home for bed rest, only for the poisoning to continue, our correspondent added.