Water Supply Connections; Thermal Expansion - Rheem GG Series Use And Care Manual

Thermal Expansion

Determine if a check valve exists in the inlet water line. Check with your local water
utility. It may have been installed in the cold water line as a separate back flow preventer, or it
may be part of a pressure reducing valve, water meter or water softener. A check valve located in
the cold water inlet line can cause what is referred to as a "closed water system". A cold
water inlet line with no check valve or back flow prevention device is referred to as an "open"
water system.
As water is heated, it expands in volume and creates an increase in the pressure within the water
system. This action is referred to as "thermal expansion". In an "open"
Drain valve
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