how fo I fix my IDEAL RESPONSE SE Boiler's 2-02 fault?

My boiler starts normally
It goes through step 0 then 1 and onto 2, where it light the flame (I know the flame lights as there is a slight increase in temperature). However after about 3 seconds it goes back to 1 then tries 2 again.
This goes on for a few more cycles of 1,2,1,2 at which point it starts flashing 2-02