Carver fitted the Fanmaster mk1 on the 3600 right up to they finished in 99/2000 so this will be the 240v heating if indeed it's fitted.
The Fanmaster uses a wall switch with five led lights, this is often next to a 'switched fuse spur' to isolate the Fanmasters 240v supply and obviously this needs to be 'on'.
It should now work and give heat on the lower two settings on the switch and the dial then sets the temperature.
Common reason for it still not working is it has overheated and tripped out. The reset switch is on the left hand end of the Fanmaster, from the front top left corner of the gas fire, it's 9ins down and 7ins back, you will need to feel for it over the back and you'l find it behind a black plastic flap, this is cut from a square plastic box covering the Fanmasters electrics.
You can download the 'Fanmaster' manual from my website www.arcsystems.biz