Disco 4 (LR4) Auxilary Heater

Hi, the auxilary heater on my discovery four doesn't seem to be working. The timer is set as it was last year yet it still doesn't come on. When I use the remote, it does all the right things, you hear a few clicks, fans and whirs for about 5 seconds and then stops. The temp is below 8, the battery is in good condition, the fuel level is good. Can anyone offer any advise on this please. Also, really dumb question but the handbook says the fuse box is under the bonnet, I can only find the one under the glove box. There is a cover similar to the battery cover but when I remove it there are pipes, wires etc but I can't see a fuse box