My glowworm spacesaver kfb has stopped working?

I fitted a new timer unit to this about a year ago and it has been running fine ever since. Off over the summer, I turned it on a couple of months ago and it was working fine. all of a sudden it has stopped working although the timer unit is still functioning. It sounds like it is on, just doesn't fire up. I can see something glowing from underneath, but apart from that, the boiler has no panel that drops down with any controls, so I can't think of anything to do. Can anyone suggest what I can try as it looks as though the problem is very simple.