Water pump problem. leaking through a pressure valve

Thank you for the tip and will try it this evening. A couple of clarifications:
1)"shut incoming water off", do you mean physically disconnect the incoming water line into the pump, or physically disconnect the output of the pump so the input to the water heater is open?
2) "open relief valve", "shut relief valve", There's no physcial switch that I'm aware of to open and shut (as far as I know). The relief valve seems to open on it's own when the pressure is too great.