Four fire engines and around 25 firefighters were called to a house fire on Cambridge Road in North Harrow.
Part of the first floor of a semi-detached house was damaged by fire. Two adults and a child left the building before the Brigade arrived and were assessed on scene by London Ambulance Service crews for smoke inhalation.
The cause of the fire is believed to have been accidental and involved a tea light candle.
A London Fire Brigade spokesperson said: "Candles are one of the most common causes of fire.
"It’s really important that you never leave a candle unattended and keep them away from curtains and anything else that can easily catch fire. They should always be kept in a sturdy fire-resistant candleholder.
"You could consider swapping your traditional candles for safer, LED flameless ones.”
The Brigade was called at 1849 and the fire was under control by 1925. Fire crews from Harrow, Northolt, Wembley and Stanmore fire stations attended the scene.