If a domestic hot water tank dropped in temperature after five minutes of use, what might be the issue?

The situation described, where a domestic hot water tank experiences a drop in temperature after just five minutes of use, points to a potential issue with the dip tube. The dip tube is responsible for directing cold water to the bottom of the tank where it can be heated. If the dip tube is broken or damaged, cold water can mix with the hot water at the top of the tank, leading to insufficient hot water supply. This would explain the rapid decrease in temperature experienced during use, as the heater could be unable to keep up with the influx of cold water.

In this scenario, it is essential to ensure the integrity of the dip tube to maintain the proper functioning of the hot water system. Evaluating other components like the gas input, mixing valve, or gas valve may be important for overall system performance, but they are less likely to directly cause the immediate drop in hot water temperature as described in this instance.