Reading your original post again, I wonder whether the problem is down to the photocell. You say when it is running you get white 'smoke' but sometimes it is colourless. This could be because although the burner is running it is not actually firing. This is a common fault with the RDB burners. Try a new photocell. They are now a different specification to the originals, and there are 2 sorts. Make sure you get the right one.