A customer complains that the hot water runs out in the middle of one shower. The water temperature coming out of the tap is 140 degrees and begins falling within one minute. After drawing water for 5 minutes, the water temperature at the bottom of the tank is measured at 130 degrees, and the burner has not come on. What is the most likely cause?

The situation described suggests that the hot water tank is not maintaining an adequate supply of hot water, given that the temperature of the water begins to drop quickly after initially being quite hot. When the water temperature at the tap starts at 140 degrees and then falls to 130 degrees after only five minutes without the burner activating, it indicates there may be an issue with how the temperature is being regulated.

A likely cause is that the temperature control is out of calibration. This would mean that the thermostat is not correctly measuring the water temperature or not functioning properly, which can lead to inadequate heating of the water when it is needed. Essentially, if the control mechanism thinks the water is sufficiently hot at a lower temperature than it actually is, it will not activate the burner to heat the water as required, resulting in a rapid depletion of hot water.

In contrast, the other options may not directly address the central issue of a thermostat problem leading to inadequate heating. For instance, the flow rate from the shower head or a broken dip tube could impact the water delivery or mixing; however, these conditions would not fully explain why the burner is not responding to the drop in temperature. Additionally, if the temperature sensor were mislocated, while it could also lead to inaccurate temperature