One morning I woke up to find that there was no hot water.
There was an ample amount of cold water, but this was in the middle of winter, so the water from the tap was actually too cold.
I sensed that the pipes were on the verge of freezing, so I turned all the taps on just a little bit, to let a tiny amount of water flow. This is the only way I know to keep pipes from freezing solid, and if that happens then they usually rupture and need to be replaced. I am not an expert when it comes to water heaters, but I know enough to check the fuel supply and the pilot light. Neither of those were the culprit, so I called a local HVAC company that offered 24/7 emergency water heater services. If this was just about my own comfort or being able to take a hot shower I would have waited, but I knew a faulty water heater could lead to a host of other problems. The HVAC tech arrived looking just as tired as I felt. On the plus side, he was able to suss out the issue with the water heater within a few minutes, but on the negative side, it wasn’t something he could fix. My water heater is connected to the natural gas pipes operated by the utility company. It turns out the company had an issue with the natural gas lines, so the problem wasn’t with my water heater, it was a lack of natural gas!