Can I ask a question please about moving and an extension

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Ok.. I am planning to move in the not to distant future, we're doing up the house at the moment. We had a two storey extension built two years ago in March. I heard that when you move you need certificates for the new boiler being installed and the electricity. My question is would the building regulations certificate which we received after the extension was built cover this or do we need to get them from the people who installed them. I hope you understand my question. Also.. what happens if the builder is now using different people and cant get in touch with the people who installed the things.. Thank you for any advice.