Four fire engines and around 25 firefighters were called to a house fire on Preston Road in Wembley.
Part of the first floor of the detached house was damaged by the fire. One woman left the property before the Brigade arrived. She was taken to hospital suffering smoke inhalation by London Ambulance Service crews.
The Brigade's fire investigators believe the fire was caused by a defective electric blanket.
A London Fire Brigade spokesperson said: "The fire started in a bedroom while the occupant was asleep.
"She heard crackling and discovered the fire at the end of the bed, called for help from other occupants and attempted to roll up and smother the bedclothes that were alight.
"A member of the public who was passing by noticed flames at the window and called the Brigade.
"On arrival, crews encountered a well developed fire in the bedroom.
"You should never try to tackle a fire yourself. Leave it to the professionals and call 999 as soon as you become aware of a fire in your home.”
The Brigade was called at 2105 and the fire was under control by 2202. Fire crews from Wembley, Stanmore, Willesden and Northolt fire stations were at the scene.