You know you didn't break it. You have your facts, stick to them.
He may well get his mate round the corner to fix it, that's his choice. As long as it is fixed, that's all that matters ultimately.
He should fix it in a reasonable time. Depending on what needs doing, that may be 1-2 weeks, but it would be that wherever you went.
It's a little vague, but case law is key here. Trust me, you're 100% in the right at this point.
If he refuses to fix, then write him a letter stating the problem and that you expect him to repair, and to reply within 7 days. If he still doesn't, then you start small claims court proceedings as it's a slam-dunk win.