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The tenant is out of luck because once he signed the lease and received the keys, he is legally bound and if he doesn't pay the rent you can sue him for breach of contract.
So you have no legal duty to refund him anything, whether he moved in or not. The fact that he changed his mind doesn't give him legal grounds to breach the lease.
If he doesn't pay the rent, you can pursue a formal eviction action in court to regain legal possession and then hold him liable for any lost rent until you re-rent the property.
IF he returns the keys and gives you a written notice that he is abandoning the property, then you wouldn't have to evict him, but you can still hold him legally responsible for all rent until you re-rent.
As an aside, in addition to being an attorney, I have also been a landlord for over 26 years...
If the property doesn't have a valid CO, then that would give the tenant grounds to avoid the lease if this got in front of a judge. But I find it highly doubtful that one non-working burner on a stove would make the property fail an inspection for a CO.
I don't have access to local city information regarding CO offices and whether they publish this information and make it available to the public.
I will opt out of the question and open it up to other experts who might have a more definitive answer for you..