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Install the T/P valve into the threaded opening at the top of the
water heater and orient the discharge tubing so that any discharge
from the valve will exit within 6 inches above, or at any distance
below the structural floor, and cannot contact any live electrical
part.
T/P Valve Discharge pipe:
1.
Must NOT be smaller in diameter than the outlet diameter of
the valve, or have any reducing couplings.
2.
Must NOT be plugged or blocked.
3.
Must be made of suitable material for hot water.
4.
Must not be over 15’ in length.
5.
Must not have more than two elbows.
6.
Must terminate at an adequate drain.
7.
Must not have a shut off valve between relief valve and tank or
relief valve and termination of discharge.
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, backflow 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 buildup 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.
