burner light comes out , but fails to light

My boiler locked out last week. After establishing gas was getting into the burner. I concluded that the igniter electrode was perhaps failed. (i had replace the igniter logic controller board last year). so it seemed next logical point of failure. 
   Removed the electrode and sure enough knackered. Installed new one , along with new igniter lead and replaced all new gaskets.

   Now the ignition goes through its sequence,  gas into burner , igniter is sparking , green burner light comes on barely for a second , but fails to ignite ? 

   Now  i am stumped .

   all input and help welcome.