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From my POV, I would say you are good. The dangerous blue and black wire are covered and yellow-green being exposed is not an issue. If you only have responsible persons in the house, you can turn it on without issues. You could also tape card board over it if you want to.
But keep in mind I’m not an electrician and give only my layman’s POV.
The silver ring below the black plastic secures the thermostat to the valve. If you loosen that screw, it will release pressure on the valve which in turn opens -> heating starts. It is rather tricky to fasten that ring again unless you can turn the thermostat to MAX though. Is the silver ring tight right now?