In article ,
JJ wrote:

Thanks to the few of you who posted suggestions. I was afraid there
might be some people warning me off of higher temperatures, but I wasn't
prepared for the mass of posts.

Thanks to the person who posted the link at http://www.rhtubs.com/104f.htm
While it doesn't give any advice about hacking the thermostat, it does
confirm that I'm not totally crazy to want the temperature hotter. And
I don't think I'm in the running for a Darwin award or likely to be put
on trial for murdering my wife. If we get too hot, we get out for a
while or turn the temp down.

From the first paragraph on that web site: "Even today, in Japan, many
public bath houses have water up to 115 ºF"

As it is now, my wife takes tubs at least 3 times a week in our indoor
jacuzzi tub (wich won't comfortably seat two) with initial water
temperatures at about 112 - measured with a thermometer. So, setting
the temp above 104 would not be anything new.

We're looking for a smaller sized hot tub - and with the amount that my
wife likes to get in the tub, it might be more energy efficient to keep
a well insulated hot tub warm than to be continually heating up the 45
ºF well water at ~40 gallons a pop.

If anyone else would like to post their advice on the easiest or most
effective way to get around the 104 degree cap, please do so.

Thanks.

-JJ

I am not an expert, and I try to refrain from playing one on usenet, and
it's quite likely that I'm wrong, more often than not. But barring any
input from someone in the biz who actually knows, I'll attempt to point
your brain in the correct direction.

I think there are three things in the temp control loop: The thermostat,
the high limit switch, and the flow sensor.

Obviously you don't want the heater running if the water isn't flowing,
because that would seriously overheat the water in the heater tube or
burn out the heater. That's a good safety feature. But some spas limit
the flow to twenty minutes at a time, which would of course shut down
the heater no matter the temp. Not a desirable feature in your case.

The high limit switch is a secondary safety device in case the
thermostat fails. Probably well hot enough for your tastes.

So that leaves the thermostat. Most likely it has an adjustment screw.
Ask the dealer. Say, "hey, what if I crank this all the way up, and it
only heats to 100? Is there an adjustment that I can use to calibrate
it?"

If adjusting the thermostat doesn't properly boil your wife, you could
short it, which would leave the heater running wide open, until the high
limit switch trips. If you wanted to get fancy, you could run it through
an external control, either on/off or adjustable. Lots of possibilities,
depending on your desires and skill level.

Uh-oh, gotta go, the thermal police are knocking on my door...