I have exactly the same problem on the same model - how did you get on with trying to fix it?
If you hold down the cook time and ready time buttons while pressing the + or - button, the gas will be ignited and the display returns to normal, but as soon as you release the cook time and ready time buttons, it reverts to no gas and an A in the display.
I am having difficulty in obtaining a relacement timer, it seems to no longer be supplied.
Dennis Parnham, January 2012