2005 Sundance 850 Optima


New member
Mar 7, 2021
Chester, CA
We got a 2005 Sundance 850 Optima spa for free from a family friend. The hot tub seems to be having issues. We have the temp set at 98 and randomly it will run up to 105 and produce OH on the screen. While in the hot tub the heater seems to be continuously running and pumping out really hot water. I know the OH means over heat per the manual; so I turn the circuit breaker off for an hour or so and turn it back on. Temp drops to 102ish and the OH goes away and then heats back up and OH returns. A few more power cycles and it seems to work fine for a while. "A While" being anywhere from a few months or a few weeks. Not completely sure what is going on. Any help would be greatly appreciated.

Thank in advance


Gold Supporter
LifeTime Supporter
TFP Guide
Jul 3, 2013
Southern OK
Pool Size
Salt Water Generator
SWG Type
CircuPool SJ-40
Welcome to TFP :)

Do you feel comfortable testing circuit's and tracing wires? If you do it sounds like the temp sensor is malfunctioning (this is a guess as we will have no idea)...

If you do not have the ability call a hot tub technician and have them fix it :)
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Reactions: Mdragger88


New member
Mar 7, 2021
Chester, CA
Thank you both for your answers. I will look into replacing the heat relay. I am jack of all trades and a master of nothing. Except being annoying, just ask my teenage daughters.


New member
Mar 7, 2021
Chester, CA
Probably not a sensor, or it would have a different error code showing as well as OH. I would say the heat relay on the circuit board is sticking.
How do I go about replacing the heater relay? Or is it the entire board? The temp is set at 98 and cranks up to over 105 but the screen will only show 105 and not shut the heater off when it hits target temp. Thank you in advance for any advice or help.


In The Industry
Mar 21, 2020
Cabool, Mo
I would bring the board to an electronics repair shop. Relay replacement is a pretty simple solder job for a pro. You can order the relays online if the shop doesn't happen to have them.
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