I sent an email to my coworker asking about a problem I was having, to clarify if it was a problem with a test I wrote or a bug in the code. I got a response saying it might be related to what he's doing, asking for the details of the problem. Because he sent it over the weekend, I didn't reply until this morning, and I haven't gotten a response since.
I'm completely stalled until I can sort this problem out, my work is completely done other than this issue, and I can't move onto other things until I finish my current task because they're connected.
In this scenario, I don't know where his desk is or what he looks like, so my only communication options are email or the company's chat program. How long should I wait before following up, and how should I approach it?