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Protection from thermal expansion

Protection from Thermal Expansion

The City of Enterprise would like to inform our customers on how to protect your water heater from thermal expansion. The City is required to have a cross-connection program in place to prevent the contamination of our drinking water. On all our new service connections and any that we have been replacing in the last ten years we have been installing meter setters that have check valves installed in them. These check valves prevent the back flow from the household plumbing system from going back into the public supply.

Protection form thermal expansion is provided in a plumbing system by the installation of a thermal expansion tank in the hot water system piping downstream of the hot water tank and a temperature and pressure relief valve (T&P Valve) at the top of the tank.

The thermal expansion tank controls the increased pressure generated within the normal operating temperature range of the water heater. The small tank with a sealed compressible air cushion provides a space to store and hold the additional expanded water volume.

The T&P Valve is the primary safety feature for the water heater. The temperature portion of the T&P Valve is designed to open and vent water to the atmosphere whenever the water temperature within the tank reaches approximately 210 degrees Fahrenheit. Venting allows cold water to enter the tank.

The pressure portion of a T&P Valve is designed to open and vent to the atmosphere whenever water pressure within the tank exceeds the pressure setting on the valve. The T&P Valve is normally pre-set at 125 psi or 150 psi.

Water heaters installed in compliance with the current plumbing code will have the required T&P Valve and thermal expansion tank. For public health protection, the City is requiring the installation of a check valve or backflow preventer downstream of the water meter. In these situations, it is essential that a T&P Valve and thermal expansion tank be properly installed and maintained in the plumbing system.

For further information contact the City of Enterprise Water Department at  541-426-3093 or a licensed plumber or the PNWS/AWWA at 877-767-2992.