An elderly couple and their daughter have been found dead in a static caravan near Camborne.
Devon and Cornwall Police has confirmed they died from suspected carbon monoxide poisoning.
Officers say the alarm was raised at just before 1pm on Saturday after the couple's helper was unable to reach them.
Firefighters visited the static caravan at Tremarle Home Park and recovered the bodies of three people and a dog from inside. The women were aged 86 and 46 and the man aged 90.
An investigation is under way, but the incident is not being treated as suspicious.
Carbon monoxide has no taste, smell or colour. The Gas Safe Register says that the most common cause of carbon monoxide poisoning results from badly fitted or faulty appliances.
The fire service says every house should have a carbon monoxide alarm. They can be bought for as little £10.
This is the second incident of carbon monoxide poisoning in Cornwall in recent weeks.
Earlier this month, Gill Adams and her three dogs were found dead at the guest house she ran in St Ives.