How Do I Purge and Re-Light a Worcester 28CDI Gas Boiler?

Is the gas back on? Yes I know its a silly question but you would be surprised. Do you have a gas cooker/hob. Light that first and watch it to make sure it stays on. If it goes out hold ignitor on or means of lighting until it relights. Then try your boiler again, it should light eventually. Failing that if the note was left by Transco or whoever the emergency service provides is in your area give them a call and get them to sort it. If they turned it off its down to them to put it back on.