The third reason a water heater relief valve leaks is
water pressure, the relief valve is set to relieve
pressure at 150 PSI (pounds per square inch) if the
water pressure in your home rises to 150 PSI the relief
valve is going to leak.
Some city or municipalities have high water pressure
from their water plants so that the water gets to
everyone on the grid.
To bring the water pressure down below the high pressure
a PRV (pressure Reducing Valve) is installed in the home
just after the main water valve, this valve can fail and
allow more pressure into your home then the water heater
relief valve can handle then you have a leak.
Also a defective pressure switch on your well pump could
allow water pressure to get too high.
So whatever caused the water pressure to get too high
after it is fixed, replace the relief valve.
And The fourth reason a water heater relief valve
leaks is thermal expansion
When water heats it expands, and water can not be
compressed, in most cases with a 50 gallon 50,000 BTU
gas water heater with a house water pressure of 50 PSI,
the water expansion will not be great enough to cause
the relief valve to leak.
With gas water heater with high recovery rates and a
higher house water pressure the possibility of thermo
expansion to 150 PSI increases, in this case an
expansion tank needs to be installed, be sure it is an
expansion tank designed for domestic water and not for a
hot water boiler, there is a big difference and the
boiler type will rust out within a year, and it is
designed for low water pressure.
Note: Under no circumstances should you plug the end
of a water heater relief valve, even temporarily, doing
so can cause your home to be totally destroyed and can
cause death to you and yours
Have it fixed by a local plumber call
Also see How to
troubleshoot an electric water heater.
Get your water heater relief valve from me it will ship
How to replace your hot water heater relief valve.