Gas Fitter Practice Test

What could cause a domestic hot water tank to drop in temperature after five minutes of use?

1. Low gas input

2. Mixing valve

3. Broken dip tube

4. Gas valve

The correct answer is: Broken dip tube

A broken dip tube can cause a domestic hot water tank to drop in temperature after just a few minutes of use because the dip tube is responsible for directing cold water to the bottom of the tank while allowing hot water to rise to the top for use. If the dip tube is damaged or broken, cold water can mix with the hot water at the top of the tank, leading to a rapid decrease in the temperature of the water available for use. When hot water is drawn for use, cold water entering the top of the tank mixes with the hot water, resulting in a noticeable drop in temperature almost immediately after usage starts. In contrast, low gas input may lead to insufficient heating over a longer period rather than an immediate temperature drop, while a mixing valve typically regulates temperature but wouldn’t cause a significant and rapid temperature drop if functioning correctly. A malfunctioning gas valve would generally affect heating and not directly cause an immediate drop in temperature as observed after just a few minutes.