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Hot overheats and shuts off intermittently


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Thanks for reading.  I'll cut to the chase as to not waste anybody's time who is kind enough to read this post.  I'm having actually 3 issues with my hot tub and I believe they are all related.  So if I can pinpoint the cause then I may possibly be able to kill 3 birds with one stone. 

The spa is a Sundance Optima, I believe year 2000.  My first issue:  I lose power to the hot tub sporadically.  The GFI breaker does NOT trip.  I am losing power somewhere in the hot tub itself.  I have tested the panel on the spa itself while it has shut off on me and there is power to the panel.  all fuses in the circuit board are fine.  I have power to the main panel of the spa.  After shutting the breaker off for about 30 minutes and then turning it back on it will repower and work fine. Only other thing I know about this is that the touch panel doesn't always function properly.  Hoping this isn't my issue because that's not a cheap repair.  

Second issue:  The hot tub is overheating.  It always heats to 106, then get the over heat code and it maintains that temperature.  I am assuming that there is a pre set limit and that's the temp it's set at?  (hi limit switch is working then?) 

Third issue:  The heated water coming out of the heater into the spa at times (not always) is hot enough to scald if you get too close.   So this tells me that possibly the circulation pump isn't pushing water through the heater fast enough?  But even if this is the case, wouldn't the spa still shut off at the desired temp (101) even if the water coming out is too hot? 

Appreciate any advice.  I'm willing to replace whatever needs it, but I hate to blow $300 bucks on a new touchscreen if that's not even causing the problems. Thanks again.

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>>>>  I lose power to the hot tub sporadically.  The GFI breaker does NOT trip

When you say you lose power to the hot tub, I'm assuming you mean the hot tub stops working, because you said there is power to the hot tub control panel.  Is that correct?

Use a voltmeter to try to determine where the power stops?  Is it at the terminal block in the control box?  Is it at the heater?  Is it at the circ pump?

Any error messages?  Four dashes perhaps?

Hi limit usually kicks in somewhere around 118 degrees, not 106.  If you're getting an overheat and the spa thinks it's at 106 degrees, the hi limit sensor may be bad.  Or the spa may really be at 118 degrees and your thermostat is bad.  Get a thermometer to check.

You should not get scalded by hot water coming out of the heater.  The hi limit sensor is mounted outside the heater, usually on the vertical side of the heater, so the water could conceivably be heating further along the pathway and not be tripping the hi limit sensor.

What kind of circ pump does your spa have?  A tiny Laing pump or a full sized 48 frame pump?   Usually, if you don't have enough pressure to move the water, you won't enable the flow switch, so the heat won't come on, so it's unlikely you'd have a reduced flow and overheat the hi limit sensor.  Unlikely but not impossible.  Same could happen from dirty filters restricting the flow.  Or some detrius stuck in the heater, or the circ pump impellar.

The first thing I'd want to know is whether or not you're getting an error message when your spa "stops."



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Actually there were dashes on the control panel when the power stops.  I didn't pay attention to how many as it never occurred to me that this was an error code of some type.  What does this mean?

Yes, when the power shuts off it won't heat, won't run pumps, no light, nothing.  Using a voltmeter I have traced power to the main terminal block.  From there it goes to a row of black boxes that  I assumed was some type of relay?  And no power anywhere past this point.  This is an old hot tub I got off of craigslist and have restored.  So I do not know if circ pump is original but it does seem to work fine and is almost whisper quiet.  When I first got it going I was getting a flo error code.  Knowing there was no debris or obstruction (took pumps apart and cleaned/re-sealed them), and that the filter was brand new, I replaced the flo switch and have never had the flo error code since and all jets and both pumps work great.

The 106 setting is fairly accurate as I can still sit in it at that temp and I'm pretty sure I couldn't handle 118. I'll look for a thermometer to put in the water to see how accurate it is.  I'm leaning toward replacing the hi limit switch since it's a fast, easy, and fairly inexpensive repair. 

Thanks for your help

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Four dashes on a Sundance Spa is a "watchdog error."  It indicates something has gone wrong and the spa is shut down to avoid hurting you.  It's usually caused by either a bad temp sensor or hi-limit sensor.  So the first question is, is the spa shutting down because the water's too hot, or is the spa shutting down the spa because it THINKS the water is too hot and one of the sensors is bad?

If it's a hot water problem, the water wouldn't be 106.  It will be closer to 118 (OK, give or take a few degrees).  That would most likely be caused by a bad temp sensor.  The temp sensor doesn't realize how hot the water is and when it gets to 118, the hi limit sensor closes the spa down to protect you.

If it's the temp sensor, the sensor is telling the circuit board the temperature's too high, even if it isn't.  One way to tell is to be looking at the control panel when it turns on.  Before the four dashes appear, what temperature does the control panel flash?  Is that number accurate compared to the thermometer you're checking with?  If the control panel says it's 118 and your thermometer says it's 104, the problem is most likely your temp sensor.

It could also be the hi limit sensor is bad.  The high limit sensor thinks the temp is 118 when it's really 102.  It shuts down the spa.  An easy way to test this is to remove the hi limit sensor from where it's mounted on the heater,  put it into a cup of ice water, then re-start the spa.  If the control panel shows any temp under 104 and then the spa turns off, it's a bad hi limit sensor.

When you get new sensors, test them before you mount them;  especially the temp sensor which is a pain to install because you need to partially drain the tub and fish the the wiring through a paper conduit.  Just connect the new sensors to the circuit board, dangle them into the water and see if it makes the problem go away.

I've never seen a tub over-heat because of a bad heating element, that probably is not the problem.  Good thing, a sensor is a lot cheaper and easier to install than a heater.


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awesome.  Thank you so much for the guidance.  I'd buy you a beer if I could.

Finding a damn thermometer suitable for this has proven to be a difficult job.  I live in the middle of freaking nowhere so running down to the local walmart or whatever isn't an option.  Will test as soon as I track one down.  The temperature that's flashing is always 106 or 107.  We have been just opening the cover for an hour or so before we get in to let it cool down some and the temp on the screen will come down to 101 or whatever then and it feels just right.   It hasn't shut off for a few days now, that's what is throwing me off.  It seems so random.  I'll test what you told me about the hi limit sensor and then probably end up replacing that first and see what happens.  I've discovered old spas are a lot like owning an old boat.  You spend 10 x more time working on them than you actually use them. lol   Thanks again.

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