baxi bermuda inset gas fire ignition problem?

have looked at the fault finder to diagnose igniter problem on my gas fire.
have replaced the pilot assembly and all leads associated with it to control box. still no spark to ignite the pilot but pilot will ignite with lit paper when when button pressed on side of fire for the ignition sequence. there are three things that could be associated with this fault and each of them are very pricy. can you help