Got same problem can hear the system go on and can hear flow and a humming noise coming from the boiler but no hot water or heating. Am I supposed to see a light/flame in the small glass viewing area? As I have nothing in there, I have tried turning the heat control knob fully anti clock wise then fully clockwise but cannot see any flame or hear any activity. I have tried pulling off the red tube and blowing into it and can hear the click on and off so that does not seem jammed. I can just see me getting somebody out and paying an extortianate amount for what maybe a easy/small job. Had the pump replaced about a year ago. Damn this boiler.
Sorry I put this in the answer by mistake should be a new question relating to same thing.

Bryan, January 2010

just repaired mine with the same fault. Check the fan is working as the bearings start sticking due to the heat. Remove the cover with the glass on and see if the fan is turning at full speed or at all. The fan activates the air switch on the bottom right (red + white tubes) which tells the PCB to light the boiler. £65
on ebay for a fan

lindeman, February 2010