Right I had a play with the jumpers.

With all the blue ones removed (they are the ones nearest the power socket) I get no clicking and no flashing LED

With the 2 x 6v jumpers in place but the one 3v jumper removed, I get the clicking but the blue USB LED on the rear flashes rather than the blue LED on the front.

With the single 3v jumper in place but the 2 6v jumpers removed I get the clicking but no LED's flashing.

So which part of my empeg is termally ill, and is it dead forever, or will it be able to rise again?