Drippy water tank
In my experience, just releasing a bit of hot water from the tank is enough to clean off the valve seat. Simply lift the lever a bit (it is spring-loaded), and let out some water. It's hot, so be careful. For safety's sake, turn off the electric heater element while you do this, to be sure the element doesn't get exposed if the tank level got too low. The dripping should clear up right away, but if not, try it one more time. If that doesn't work, it may be time for another pressure-temperature valve.