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The hottest most spas will get now days is 104* Jacuzzi and Sundance use to be able to go up to 108 with a special chip but no longer. I think you can thank the government for that one??
You can thank the UL standards.There is a plus/minus on that 104. Set spa for 104 and see what it does.A well insulated spa will heat just by running the jet pump with the cover on; the heat cannot escape. Try setting at 104 and see if you like it. If not, try running the pump(s) with the cover on. Check in an hour and see how hot it got.
More likely the lawyers.