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.
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.
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