Two tests should be all you need. First check for 240 volts at the element. If it has 240 volts use an ammeter to see if it is drawing current. If it is above 15 amps then it is heating if it is zero the element is bad. If it is heating and you do not have hot water, and if you have a concrete slab floor, then you have a hot water leak under the floor that is draining the water faster than the heater can heat it.