Two fire engines and 10 firefighters were called to a suspected carbon monoxide leak in Golden Manor, Hanwell.
The Brigade was called after two people reporting feeling unwell with symptoms of carbon monoxide poisoning.
Two adults and a child were treated at the scene before being taken to hospital as a precaution by London Ambulance Service crews.
Fire crews wearing breathing apparatus carried out a sweep of the flat and boiler room and found no elevated readings.
The Brigade was called at 0651 and the incident was over at 0850. Fire crews from Ealing and Southall fire stations attended the scene.