how do i relight the pilot light?

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 Combi 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. I have reset the pressure gauge to read just under 2.Can anyone help?