TURN IT OFF IMMEDIATELY AND CALL A REGISTERED ENGINEER, if the flame is licking out of the front it indicates a blocked Heat Exchanger, and will be releasing CARBON MONOXIDE into the ROOM
In fact if the amount of CO was high enough you wouldn't have had enough time to boot up your computer!!! FOR YOUR SAFETY..DO NOT IGNORE THIS WARNING!
www.elanar.co.uk, September 2009