The home-owners were woken by their smoke alarm in the early hours.
Two fire engines with nine firefighters and six on-call crew were called to the St Saviour property at 3.50am (8 September).
When they arrived a 'fully developed' fire had engulfed the first floor of the home.
The crew managed to knock back the fire before going inside with breathing apparatus and fully extinguishing the fire.
No one was injured.
The fire service says the incident highlights the importance of having a working smoke alarm.
The cause of the fire is still being investigated.

Nowacki wins Jersey’s first Commonwealth Games medal in 36 years
Thousands expected at Havre Des Pas Festival this weekend
Commonwealth Games: Nowacki into 100m breaststroke final
Channel Islands face 'physical' Poland test
Price of heating oil and other fuel increase by more than half in a year
Man jailed for importing nearly £600k worth of cannabis in bumpers of his car
Baby born on Guernsey's Marine Ambulance
Drug trafficker who claimed he was the ‘Accredited Dealer' jailed