Hello please help,

I have a Tiger River Spa Watkins Sumatran N, with a No Fault heater (IHH-6000-NHCW)

I recently went out and found it cold. Called tech at the spa shop and he told me to take filter out and cut power and turn it back on to reset the heater. DID not work.

Then I drained it because it needed it. With no water and power off hit the reset button in the heating element. Filled back up with water. Did not work.

Realized that it probably needs water to reset properly. Hit the reset button again. Still does not work.

Took off panel to the motherboard to see if anything looked burnt. Looks fine. LED lights indicators are as follows.
LIM yellow light on
HRT red light on
Control Unplugged light off

Next step to me would be to use a voltmeter to test Heater not sure how to go about it. Also, I would like to test the Relay if need ed. would like some direction to go from someone more familiar please

thankyou chris