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Page 9
Closed system thermal expansion:
Periodic discharge of the T/P relief valve or failure of the element gasket may be due to thermal expansion
in a closed water supply system. The water utility supply meter may contain a check valve, back ow
preventer or water pressure reducing valve which will create a closed water system. During the heating
cycle of the water heater, the heated water expands causing pressure inside the water heater to increase.
The T/P relief valve may discharge hot water under these conditions which results in a loss of energy and
a build up of lime on the relief valve seat.
To prevent this from happening, there are two recommendations:
1. Install a diaphragm-type domestic hot water expansion tank (suitable for potable water) on the
cold water supply line. The expansion tank must have a minimum capacity of 1.5 U.S. gallons for
every 50 gallons of stored water.
2. Install a 125 PSI pressure relief valve in the cold water supply line. Make sure the discharge
of this valve is directed to an open drain and protected from freezing. Contact your local
water utility or plumbing inspector for information on how to control this situation. Never plug the
outlet of the relief valve.
Filling the heater
Caution : Before plugging in the water heater power cord into an outlet, be sure that the system is
completely charged with water and all air is removed. Before connecting the power, ll the tank and system
with water and check for leaks. To be sure that all air is out of the water system, open the hot water
faucets on your xtures until constant water ows from them. Otherwise any air remaining in the tank will
cause the water heater element to self destruct.
Filling the water heater:
1. Open the hot water faucet.
2. Open the cold water supply valve.
3. When continuous water ows out of the faucet, the tank is lled.
4. Close the hot water faucet.
5. Check entire system for leaks.
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