You check for 240 volts at the element terminals and if there is 240 volts, then you use an ammeter to see if it is drawing any current. If yes to both tests, then the element is Okay, unless one wire is drawing more current than the other or current is being used when the element should be off. You test the thermostats after the heater is full of hot water by rotating the control dial and checking to see if the circuit opens and shuts off the element.: How do I test heating elements and thermostat to see if they are bad on a hot water tank?