Four fire engines and around 25 firefighters were called to a house fire on Croydon Road in Croydon.
Most of the first floor of a two-storey mid-terraced house was damaged by the blaze.
There were no reports of any injuries.
The Brigade was called at 1532 and the fire was under control by 1614. Fire crews from Croydon, Purley, and Norbury fire stations attended the scene.
The Brigade's fire investigators believe the fire was caused by a fault in an immersion heater in a boiler.