Thermal Expansion – Perhaps you have heard the term and not understood how it can affect your plumbing system.
Basically, when water is heated it expands.
For example 90°F water heated to 140°F in a 40 gallon water heater will expand by almost ½ gallon. Where does that water go? Water is not compressible; the extra volume created by expansion must go someplace. When the system is active (toilets flushing, doing laundry, washing dishes, etc) this extra volume is not noticed. But, during periods of inactivity (gone to work, sleeping) the system is closed and some potentially dangerous problems can arise. Improperly positioned check valves (one way valves) can make this situation even more dangerous. During no-flow periods the result of thermal expansion is an increase in your water pressure. If you live in low to moderate pressure area this increase in pressure will rarely be noticeable and doesn’t pose much of a threat. Those who already have high pressure being delivered to their homes might notice some annoying symptoms such as: pressure surges, dripping at the water heater relief valve, running toilets and faucets. More serious symptoms can also occur such as: ruptured or distorted heater tanks, burst pipes and valves.
If you are in a high water pressure area(>80psi) it is important that you have a pressure regulating device on your system and that you test it regularly to see if it is working. When we visit a home to perform service we regularly take pressure readings so we can advise the owner if any potential problems exist.