One morning I woke up to find that there was no hot water.
There was an ample amount of frosty 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 cold, 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 suppose to keep pipes from cold solid, & if that happens then they usually rupture & need to be replaced. I am not an expert when it comes to water heaters, but I suppose enough to check the fuel supply & the pilot light, then neither of those were the culprit, so I called a local Heating & A/C company that offered 24/7 emergency water oil furnace 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 oil furnace could lead to a host of other problems. The Heating & A/C tech arrived looking just as tired as I felt, however on the plus side, he was able to suss out the issue with the water oil furnace within a few minutes, but on the disadvantage side, it wasn’t something he could fix, but my water oil furnace is linked 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!