Tankless Water Heater Explosion

While investigating the cause of a tankless water heater explosion, the extent of the damage reinforced the mechanics behind the explosive force. Tankless water heaters are devices that put a large amount of heat into flowing water in a very short period of time. But, when the water stops flowing and the heat doesn’t, there can be a tremendous release of destructive energy. It is well known that as water is  heated in an enclosure, not only does the temperature rise but, the pressure also rises as well. Pressure cookers are a good example of how water can become pressurized and if caution is not exercised by the user, can be come a deadly force. In addition, explosions involving conventional water heaters and boilers are not unheard of. As a result, temperature and  pressure valves have been required equipment on these items for a number of  years. However, tankless water heaters don’t have relief valves. Since the amount of water to be heated is less than one gallon, (when water is not flowing) it doen’t take long to cause the temperature and pressure  to reach explosive levels. The tankless unit currently under investigation contains two small reservoirs in which heating elements are immersed. The reservoirs appear to be constructed of  a hard, plastic-like material, the properties of which are unknown. The point at which rupture occurs is  dependant on the properties of the material because it is the materal that is  subjected to the rapidly increasing pressure.