boiler not firing

I have posted this to uk.d.i.y as well.
I have a Potterton Suprima 40 boiler which was serviced recently. I can't get a hold of the company just now because they are shut till morning but I though somebody on here might be able to help. Basically the boiler is having problems firing up. This is a recent problem, after the service it seemed to work okay. The pumps are all spinning in the pipework and appear to be okay. When the bolier goes to fire, the pump inside the unit spins up and the ignition can be seen sparking away through the small window, but the burner fails to ignite. The boiler then shuts down and tries twice more.
It fails no matter if I use auto timers or switch it on manually. Occasionally I can get it to ignite if I hit the reset button a few times. I've managed to convince myself that the blue ignition spark is not as bright as it used to be, but this may be a red herring. Can the part of the ignition that provides the spark become worn out?
The boiler is a conventional ( non combi) gas fired. Any thoughts? By the way, when I do get it working, the radiators heat up and I get hot water as normal.
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