This test is best done with the heater installed and water in the hot tub. If the element is not wet, the test to ground can fail and make you think that the heater is okay!
Please evaluate your skill level before attempting this test. All tests performed by you are at your own risk
Power Off At Breaker
Disconnect heater element from any wires attached to it. Be careful when unscrewing the nut holding the wires in place on the element, you do not want to twist the “cold pin” that leads to the element. There is usually a fixed nut below the removeable one that will allow you to secure the cold pin.
It is not necessary to remove the heater assembly! You want water in the heater manifold during this test!
With your meter set on the most sensitive ” ohms” setting (the OMEGA symbol on the meter) put one probe on one element lead and the other probe on the other lead.
If you meter does not change,it is showing no continuity, the element is bad
If your meter measures resistance then it is showing continuity which indicates the filament inside is intact, but the heater could still be bad!
Ground Fault Test
Move one probe to a metal part on the heater casing leaving the other one on one pole of the heater element . If there is any flicker of continuity from one element lead to the heater casing (ground) the element is bad, even though you may have tested good continuity above! This is a ground fault situation and is what your GFCI is picking up and saving you from!
If you have an intact filament and no fault to ground, the heater element should be good and you may have a different problem.
Since gfci’s are very sensitive, you could still have a bad element and your meter sensitivity may not be allowing you to pick up the fault.
Okay it’s bad, now what do I do?
Now you need to replace the element (if replaceable) or the entire heater assembly.
The most common replacement element is the flow through element. If your heater manifold is a stainless steel straight flow through tube, this is the element you’ll need.