What are the Causes of Overheating in Hot Water Systems?

December 12, 2019

No question about it, overheating hot water systems must be checked out as soon as the problem makes itself known. If someone is at risk of being scalded by their shower water, then the issue must be addressed and rectified right away. If a blast of eye-stinging steam comes rolling off of a tub full of bathwater, the problem simply cannot go ignored. Let’s get moving, why would this normally reliable equipment produce dangerously overheated water?

Check the Tank Thermostat

Located in a garage, utility closet, or some other well-vented storage area, the tank will be mounted securely on a solid base. A cold water pipe enters the system, then a hot water pipe exits at a higher point on the same tank. Controlling the electric elements or the gas burner, a thermostat turns off the heat source when the tank water reaches a predetermined maximum. If the thermostat is set too high, the tank water will become scorching hot. Tweak this water temperature controller downwards if the water is dangerously hot. A 70°C max is advised. By the way, the temperature can’t go too low, not if it’s to kill unhealthy bacteria. Typically, on domestic systems, there’ll be a high and low-temperature thermostat. Repair techs usually pull out their digital voltmeters when they suspect a damaged thermostat.

Mixer and Pressure Relief Valve Malfunctions

Plumbers wish real-life hot water systems were a simple as the layout described above. In reality, however, there are buffer tanks and thermostatic valves, recirculation pipes and dip tubes, plus who knows however many supplementary subsystems, too. If that thermostatic valve doesn’t mix the cold and hot water properly, scalding risks materialize. If a pressure relief valve sticks, and this is an extremely dangerous scenario, then the strangulated steam heat echoes back into the main hot water line. Again, skin damage is a likely repercussion here, as is a possible system rupture. That’s why pressure relief valves, the system’s most important safety feature, must be maintained. By the way, if this is a gas-fuelled burner, it’s the gas valve assembly that’ll need checking.

At any rate, most if not all of these problems are correctable. A maintenance check will inspect a hot water system for thermostat misbehaviours and valve malfunctions. The inspection will also look for possible mineral build-ups. If that high mineral content, as caused by a local hard water issue, settles to the bottom of a hot water storage tank, then it’ll act as a burner insulant. Electric elements and gas burners are forced to work harder when these coatings accumulate. If the build-up were to suddenly clear, the excess thermal energies would cause the system to experience a sudden thermal spike. Again, this overheating water threatens the skin and soft tissues of unwary bathers.

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