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.

'Arrive at work feeling more positive'
Profits rise at CI Co-op
Police Chief blasts 'unacceptable' levels of drink-driving
Trio of Laureates lined up for Jersey Festival of Words
Recovery Hub website offers free mental health courses
Jersey and Guernsey both lift trophies in Siam and Muratti weekend
Islanders encouraged to foster with new model of support
International blues musicians play Royal Square for free