HOT SPRINGS JETSETTER MODEL J 1996 115VAC
HAS WATKINS "NOFAULT 6000" HEATER THAT LOOKS TO BE A REPLACEMENT. AFTER YEARS OF SATISFACTORY SERVICE, CONTROLS WILL NOT RAISE WATER TEMPERATURE OVER 100 DEGREES. HEATER UNIT GETS HOT, HI LIMIT NOT TRIPPED. FOUND WIRING FROM TWO SENSORS MOUNTED IN WELLS ADJACENT TO HEATER -- JIGGLED PLUG-IN CONNECTORS ON SIDE OF METAL CONTROLS PANEL, AND NOTED THAT THE HEATER DID START UP. CAME BACK LATER AND UNIT IS DEAD. NO FUNCTION OF CIRCULATING PUMP, NO HEAT, NO MAIN PUMP.
POWER IS OK.

WHAT ARE THE TWO SENSORS? ARE THE CIRCUIT BOARDS INSIDE KNOWN TO FAIL EASILY? -- SEEMS LIKE A PROBLEM WITH SENSORS.

I DO NOT SEE ANY CAPILLARY TUBE, AND WONDER IF THIS UNIT HAS AN ELECTRONIC THERMOSTAT SENSOR?

A WIRING DIAGRAM WOULD BE A GREAT HELP.

Those are your high temperature limit (protective), and your normal temperature sensor.

I wouldn't normally suspect the board because obviously it was still working and regulating the temperature, only the maximum it would sustain is 100 degrees.

Sounds like it's time to replace the sensors. (You played with them and they finally died?). Bad sensors can keep a digitally controlled tub from working (depending on the software on the board). See if you've got a local dealer that's got the sensors in stock, replace them and it if it works... no more problem. Otherwise, time to start suspecting something else.

For what it's worth, it is normal for these sensors to wear out. (Almost 10 years running sounds like you got your money's worth out of'em.)