Gents.
I have had the same problem - water circulation pump started but burner failed to ignite. After investogation
I have found a fan is not spinning. As a short term remedy - remove 3 metal clpis holding the fan and shake fan assembly [BEWARE: 1. Disconnect power supply; 2. motor is HOT!!!]. attached clips again and after start fan is able to spin.
Fan must run and it is confirmed by flow sensor [the white element at bottom right of the boiler with 2 hoses coming from the top] before burner is ignited.
Manual for the boiler can be found at
http://www.r-and-m.co.uk/Downloads/24iInstallationManual%5B1%5D.pdf
Piotr
January 2011