1994 D1 Quadra Upper Control Panel

Greetings,
I have a 1994 (yes it's old) Dimension One Quadra Hot Tub. Recently, the heating element stays on and the tub gets too hot. We had some binding of the temperature dial on the upper control panel, and now it turns very freely. I think the dial/variable resistor (?) may have failed. This tub has two temperature sensors; one for the tub and one for freeze protection which is attached to the heater tube. With the water at 97F, the tub sensor reads 19.4 Kohms and the other reads about 18.4 Kohms with the tub off and not having been circulated since overnight (air temp about 50F). In another post here, it was mentioned that these are not likely the standard 10Kohm sensors. So, I think since both are reading about the same, they are probably OK?

This makes me think the issue is that the temperature dial on the upper control board (see picture) is faulty. It seems this upper control board may be difficult to find
(D1 Spa Upper Control Panel – 01560-118), and I'm not sure how to test is since it plugs into the main control board with RJ12 phone connectors. It's not obvious which leads go to the temperature dial.

Any thoughts on how I can test the dial? If I remove the upper control board is it possible to swap out the assumed variable resistor? Any other thoughts or source for the upper control board. Looks like the upper control board would just pry out of its fitting?

Thanks,

Mike
 

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I need to see the circuit board/wiring diagram.
The spa overheating and triggering errors is likely a stuck relay on the board, the topside is just buttons and a dial. When first started does it OH within minutes or does it run for a while?
The sensors are temp and high-limit (overheat), there is no ambient air temp sensor in a portable spa. This tub has a sensor in the plumbing or shell away from the heater, so some temp variance is expected even when off for a period. That said, sensors are cheap and fail regularly so it might be worth getting some new ones anyway.
I might have that topside.
 
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