Hot Tub Thermostat adjust

HOw can I trick the thermostat on my Marquis Spa, so that I can heat the water to higher than 104 degrees? I have heard of some people dipping the thermostat in silicon, which would work, I guess, but that sounds rather inexact. I would prefer a way to trick the temp gauge into thinking it was colder than it really is. I want to get the tub up to about 107.
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You can't. That's the upper temperature limit for UL approval :-)

The latest Marquis Coastal Reward spas use a Balboa M7 controller with 2 thermistors near the heater. Balboa says the first (as water flows by) controls the water temp and the second is a 118 F safety limit. They must agree within 2 F for the controller to work.
If you wanted to make the controller think the water is 104 F when it's really 110, you might put a resistor in series with each thermistor near the control board. They have a negative tempco, with 22117 ohms at 90 F, 17636 at 100, and 14158 at 110, so 104 F would make them about 16245 ohms, like a 2.2K ohm resistor in series with each 110 F thermistor.
Nick
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Nick, I was able to do as you suggested, and it worked out perfectly! Thank you so much for your time, and expertise. Marcia
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