An elderly couple woke up in the early hours to find their home smoke-logged after a fire broke out in a bedroom.
Firefighters said a microwavable hand warmer caught fire after being left on a mattress.
The couple discovered the fire in their home in Sale Hill, Broomhill, at 1.40am and raised the alarm.
When firefighters arrived the man and woman were at their door.
They did not require hospital treatment.