Agree with Damian, originally both Carver and Truma used a 12v fan on the back of the gas fire for blown heating. Carver were then the first building 240v heating elements into the fan unit,(Fanmaster mk1),this could use either but not both. Later, (1998), they used seperate elements with a fan so gas, electic or both could be used,(Fanmaster mk2).
The current Truma version,(gas fire + ultra-heat),is more or Less the same as the mk2 Fanmaster.