Maybe if you said what you actually want to know or do you just expect us to tell you step by step what to do, read the instructions that is what they are there for and @undertrained is correct you shouldnt be removing the combustion cover which on that boiler you have to in order to access the wiring terminals
If you are, then you should be asking in the CC, not in a public forum. It’s not nonsense, it’s a legitimate reply. As @ianmcd said, read the instructions.
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