Myson orion 40si?

Hi there!
I have a myson orion 40si
The problem i'm having,
When the the system fires up it will take 3 to 8 attemps to light.
Works perfect when it lit.

This is a list of things that have been changed
1. New gas valve
2. New fan assembly
3. New ignition board
4. New spark electrode

What else can I do? Please help?
Many thanks David