I have a Dimension One Aurora Spa (2002), and the "High Limit Sensor - Do Not Enter Water. Call for Service" message came on the digital read out. The temperature of the spa is 90 degrees, and the outside temperature is around the same. Can you help me determine what is wrong, and how to fix it (besides calling service)? Thank you.

I'd first try replacing the hi limit sensor. Follow the wire from the terminal on the board to the sensor - should be easy to find.

Do you sell parts? If so, can I order a High Limit Sensor from you? I understand they are $23.95. Is shipping/handling free? We have a 2001 Dimension One Aurora.

I don't sell anything. I, like you, own a spa I try to keep running.
Since the people who maintain this site rarely see fit to answer questions here is my recommendation.

I have found that Easy Spa Parts is an authorized parts dealer for Dimension One Spas. Good people.
Call Phil at Easy Spa Parts
866.418.1840 toll free

I have a dimension one ultralite 2. I replaced the high limit sensor but I still get the same message. When I first started the spa up the temperature reading went up to 109 degrees then dropped down to 64 degrees which was the water temp. Then the high limit sensor warning came on and I am back to no heat. Any help would be appreciated.

I too, am having similar problems with a sundance jaccuzzi spa. You may just have an airlock iin your circ pump, or whichever pump works with the heater. If water is not circulating, the heater hi limit, or flow switch, or some other device will detect it and shut it down. The first thing is to get the manual for your tub. Download it, or buy it if need be. There will be a troubleshooting guide inside that will help.
It costs nothing to turn off the spa and check all the fuses with a continuity tester. It also is worth taking the various pump unions and actually look inside to see that the impeller is not broken, or clogged with hair or foreign objects which will restrict the flow. You may want to run it without the filters, but be sure no foreign objects can get sucked into the pumps first. Run it with no filters. If it works, you may just need to clean or replace it/them.
Hope this helps.
I have just bought many parts for nothing and wound up removing the circuit board and sending it in for service. Hopefully, your problem is much more simple.
Last month I spent 12 hours on a spa and finallly found a sponge was lodged in the intake of the circ pump. The customer had assured me that she never ran it without a filter. Look for the obvious, even if it means taking thing apart and looking inside with a mirror. The water must flow freely through the filters, into the pump, out of the pump, through the heater and back into the tub. That reminds me. Sometimes all, or most of the jet valves have been turned off and this is enough restriction to cause a problem. Make sure they are open and pumping water.
Good luck.

Let the spa cool down by turning off the breaker for an hour or so or 98 degrees preferably. As other have suggested, check for the obvious/unobvious first. Measure the water temp with a digital thermometer from your medicine cabinet. It is very accurate and will tell you if the thermal probe (high limit sensor) is functioning accurately. If it is within 1 degree I doubt it is the cause. I stated 98 degrees because you are in the range of the thermometer for measuring for a fever. Turn the breaker back on and set the temperature until the heater light on the control pad goes off. Take a meter and check to see if the 2 legs have voltage on the heater tube. If you have voltage when the LED for heat is off you have a bad relay. If it is a Gecko board, I have posted the new part number for the AZ2150 relay. Digi-Key has them for $2.75 EA. The relays seem to be the weak link due to the load from the heater on the contacts. The relay can be replaced in about an hour if you are good with desoldering on a PCB board.

Hope this helps others with the problem I had. This is my 1st hot tub and the logic is easy to follow.

MAK