Is the fan running.the bearings can seize and if the fan aint running then the gas valve wont open.
You need to take the front off the burner to see the fan, isolate the gas so that the burner doesnt light and singe your particles.
If you open a tap then the fan should run before the gas valve opens.Make sure you dont touch the fan while you have the cover off as it is live and all the motor is exposed.
graeme myers
April 2008