No hot water?

Yesterday my mother and I heard a pop, and we couldn’t figure out what it was to save our lives. And now that we try to bathe and all, it turns out there’s no hot water. So I’m curious if it was a malfunction with the water heater. I’m not familiar with any of those types of things, but if someone is, could you give some ideas? We did call maintenance but the soonest they can come is on Wednesday.