Hottub do not heat above 82F

[serge9898]

Hi,

I have a Hotspring Jetsetter (Model J)
The Red Power light is on. the Green Ready light is on until 82F. If I select 83F and temperatures above 83F, the Ready lamp is off. No blinking lamps.
And the water remains warm (after a week it reaches about 90F)

Thanks to Amos' help: We found a fried relay contacts. I fixed the relay board with a new relay. (The old relay still worked and the new one works...)
I checked the voltage out of the relay board: It sends 110V to the heater.

The heater doesn't heat much: Water out of the pump is just warm (~90F) not hot. But not completely cold.
The 2 LED on the controller board are on (LIM OK & HEATER ON)

I measured the resistance of the heater and I found 0 Ohms! (I was expecting 9 Ohms... R=V/I. 6kw)  
But I plugged the heater directly in the 110V with a cord I created: The breaker did not trip.

What do I check next?

I guess I need to get a better multimeter and do an amp reading on the heater right?

Or The High-Limit Thermistor?

Thanks for your help
Pictures posted here: https://sfbay.craigslist.org/sby/wan/6099854006.html

[Jersey Hot Tub Repair]

If there's no continuity through the heater, the element is bad. 

[Tperk]

Get a clip on multimeter to put on one of the 2 heater wires going to the relay board. Not sure what current should be for a 110V tub, but usually a 230V tub will draw about 18 amps when the heater turns on.