My pilot light on boiler has gonme out and dont know how to put it back on?

I have a potterton profile 50e. my heating system wont come on, when i switch it on the pilot light doesnt come on. how can i get my pilot light to come on?usually when you switch it on you can hear the tick tick noise of the pilot sparking up, but when i switch it on you can only hear the noise of the system starting up, but with no pilot light, the heating doesnt come on and also therefore have no hot water