Depending on the amount of venting, it could be a failing relief valve, excessive house pressure, thermal pressure buildup due to a PRV or check valve in the supply line, over heating due to bad thermostat or element. So you can see that you have a shopping bag of possible options, but replacing the relief valve would be the first one since they should be replaced every three or four years anyway.: Occasional venting from relief valve. : Have 15-yr-old State, model Courier electric. : Anyone have idea: thermostat, element, relief valve?