MinuteHE gas boiler, water pressure

I'm getting an error 34 when I turn on the heating. I think that means there is no water in the boiler and it won't turn on as a result.

I have a copper pipe coming out of the boiler and a silver flex pipe. I'm pretty sure the other three are to do with gas and rads. The silver flex pipe seems to be going to the waste pipe on washing machine (connects to PVC pipe). The copper pipe is about a half inch thick, has a yellow nob, two yellow handles and a white twisty thing (sorry can't think of name ) there is also something on top of boiler which I think is a bleed valve.

I'm thinking I should just try and bleed the valve on top? Sorry I'm on iphone and don't know how to add pictures with the stupid thing... I'm cold