My gas vaillant ecotec plus 831 boiler won't start?

My gas ran out, I put some in an got the supply back on again, I tried to restart it but it won't so I opened the two valves to try an real ease pressure which I was shown to do before but it won't restart there's an x through the flame an I'v no warm water or radiators heating up, I think the pressure gage has gone too high as it's near the red at the top how do I get it back down an restart it