User Manual

10
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, 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 150 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.