Wrote what follows below elsewhere and in answer to the same question, and if there is a reset button somewhere to press?
In this case it was indeed my first thought, that being not the 10A fuse, but it's holder within the isolation switch and actually quite a common fault?
First there is no reset to press on Truma electric heating, there are though two over temperature thermostats. One is self resetting when the heater cools, the other holds itself off until you switch off the mains supply to the heater, only then can it cool down and reset itself automatically.
This one can sometimes break up and prevent any power getting to the elements but none of the above should affect the green light
The clue then is the green light on the switch, this is powered by it's own little 12v transformer on the heaters control board at the back of the fire, it relies then on 240v getting to the control board.
A poor connection is the most obvious, doubtful it's on the control board itself so I would first take a look at the mains isolation switch.
These contain a fuse and the fuse holder does seem to have a habit of melting and eventually breaking the connection, your's then might be on the way out hence you see the green light for a brief moment?
After that I would suspect the transformer itself, quite common for these to burn out.
There is also the slightest chance the wiring loom to the switch has come loose but I very much doubt that.