Several months ago a plumber fixed a water leak in our front yard. Since then the water heater leaked from the pressure valve. We replaced the valve, but it still leaked. We replaced the thermostats, but it still leaked. We replaced the water heater and now the NEW one is doing the same thing. What is the problem? Why did the heater only begin to leak after the leak in the yard was fixed. Any help would be greatly appreciated. Thank you!