Two appliances and crews from Aylesbury attended.
The fire, on the kitchen hob of a three-story house, was extinguished before they arrived.
The firefighters used a thermal imaging camera and a gas monitor.
One woman, one man, and one child, who had all been exposed to carbon monoxide were passed into the care of South Central Ambulance Service.
Find out more about the signs and symptoms of carbon monoxide poisoning in our Safety Advice Hub.