is the 12 volt blower fan working? Perhaps the heater is working but getting too hot locally as there is no air flow to move the heat out of the back of the fire.
Dave.
------------- Give a man a fish and he will eat for a day,
Teach a man to fish and you can get rid of him for a whole weekend.
That sounds like a strange fault Rob, even if only the 500W section was working you would feel some heat coming out with the fan turned low.
The baffling part is that something is getting very hot, my guess is the crimp connectors to, and/or the overtemp cut-outs, they have a habit of arcing and burning out over time, maybe shorting to earth now hence the tripping. Unfortunately it sounds like a bit of a strip down and maybe professional intervension.
Dave.
------------- Give a man a fish and he will eat for a day,
Teach a man to fish and you can get rid of him for a whole weekend.