No display on Ferroli Optimax HE 31 C control panel why?

Please help. The control panel has some lines on it (power is on) but no symbols at all - no fault codes, no pictures of taps, nothing. The water pressure was low so I've refilled the boiler. I've bled the radiators - no air. I've tried resetting the boiler - no joy. I've tried switching it off then on again - no joy. The boiler is making a noise like someone snoring! That same rhthymical noise like a bubbling or vibrating noise, but on then off, on then off - just like a snorer!

The manual says something about opening the gas cock to purge the air upstream of the gas valve but I'm not sure which valve I'm supposed to be opening!

Help! I have a new baby and no hot water.