You need to do the following Turn off the water to the water heater. See if the leak stops. Check the pressure at a hose bib with the water off to the heater. If it is still 140 or so you have a failed pressure reducing valve. A pressure reducing valve creates a closed system and you need an expansion tank installed somewhere on the cold line between the water heater and main shutoff valve as well as replacing the PRV. Most expansion tanks are located somewhere over the heater on the cold side betwee the tank and tank shutoff.