Yes instant damage is done due to the over rated fuses commonly used in caravans, this means the track on the switches printed circuit board, (being weaker than the fitted fuse), becomes the fuse and burns out.
Carver rated the fanmaster 12v circuit at 5amps, while infact it runs happily on my 1amp fused test lead, I therefore always recommend independently fusing the Fanmaster at 2amps to prevent this type damage.
Sadly if you have automatic electronic ignition on the carver gas fire and presumably on the same circuit?, it will have had that as well and also now in need of repair!
PS I can of course repair your switch/ignition module