How do you relight the boiler?

I had to turn off my water to exchange a radiator, on turning the water back on I am unable to get hot water. I checked the Ariston Euro Bombi boiler and no lights were on, even though when I turn the thermostat I can hear the boiler which shows the boiler is turned on, but still no display lights even after pressing the on/off switch. I am also unable to get the pilot lght started even after pressing the reset button but think this is because theres no display lights to show the unit is on. Can anyone help?