How can i fix my Potterton Netaheat profile 40e?

I have just moved into a new property and the pilot light on my potterton Boiler won't come on when the timer unit asks it to. It does work occasionally but not everytime and seems to be getting worse. I can light the pilot manually using the reset button and it comes on with no problem at all. The boiler will also turns off when the timer unit tells it to. The boiler is only 4 years old.

Can anyone shed any light on the situation please?