Pgae 7 of this pdf...
http://theinitiativegroup.org.uk/fscinitiativedatabase/Baxi/BaxiCombi80e105e.pdf
Says Fuse 2A Fast Blow to BS 4365
Fuses often have the rating stamped on the silver end cap
A hobby electrical shop like Maplins will be a good source for a new fuse but the fuse may well have blown for a reason... It appears to be in series with the external 3A fuse and all AC power passes through it.
Good luck...
Peccavi, July 2009
