"The Temperature and Pressure Relief (TPR) valve on your water heater is a ... If the valve continues to leak, Mazzacone ...

Once the temperature and pressure relief valve at the water heater leaks, go check the pressure gauge. If the 'surge indicator' shows something at or near 150 psi, the problem is excessive pressure.

If the pressure relief valve on a boiler system chronically leaks, even after replacement, it probably means there is a problem with the expansion tank. Reuben Saltzman, Structure Tech Home ...

the higher water fill pressure will overcome the standard 12-psig air charge in the tank and partially fill it with fluid. When the system heats up, there may not be enough room in the expansion tank ...