Thermal expansion is a dangerous increase in water pressure due to heated water having nowhere to go in a closed system. All backflow prevention devices and many water meters are manufactured with check valves in them to prevent water from flowing in reverse and into our water system. The valves are a safety feature that protects the city water supply from contamination; however, they create a closed water system.
The closed system is not a problem until water is heated with little or no space for expansion. The result is a dangerous increase in water pressure that can damage water heaters, plumbing systems and fixtures. Thermal expansion may lead to more serious problems and may also contribute to water heater ruptures and in rare cases explosions. But, there’s a solution!