Logic Question for OH error on 2001 Sundance 850 series

[HomePC]

I've been getting a random "OH" error on my display board recently. It will go away after a while. I can't operate the 2-speed pump on high speed when this error is flashing (I assume this is by design). I believe this board has 3 sensors (hi-limit, temp, flo). I believe this board has 3 relays, in series, that provide power to the heater when all are closed. One relay for each sensor, I think. My question is: does the fact that the "OH" displays on the Control Panel display indicate the 'high-limit" sensor itself is working but one of the relays is stuck closed when it should've opened? I'm thinking I have a stuck (closed) relay (temp-sensor). Is it possible the "temp" sensor is not opening when it should causing the "high-limit" sensor to act as it should which in turn causes the "OH" error? I know the flow switch is okay. Thoughts?

 

[CanadianSpaTech]

Need more information. What brand, year and model of spa. Post pics of the circuit board and the schematic on the inside cover of the spa pack. There are many potential reasons for an OH error.

Is the actual water temp going above 110?

Dirty filters can slow the flow of water through the heater tube and cause an OH error... sometimes intermittently. Remove your filters and leave them out until the issue is fixed. Take them out of the equation. 

Could be a pump issue especially if you have a small magnetic drive Laing Circulation pump. They are notorious for starting and stopping.

To many closed jets will also slow the flow of water. 

Partially closed gate/slice valves can again slow the flow of water causing the slow moving water in the heater to quickly rise above 110 and send an OH code.

Clogged jets... This really only pertains to hot tubs that have a separate circulation pump that runs 24/7. If the hot tub is older and has run for many years calcium can form on the heating element and when the build up reaches a certain size chunks can break loose. When they break loose they will either be pushed into the hot tub if small enough to pass through the plumbing or if bigger will get trapped in the plumbing just behind the jets. If enough calcium chunks build up behind the jets it will restrict the flow through the heater below the 25 gallons a minute required for the M7 heater with the sensors. With the flow reduced the heater will still be heating but the water inside the heater tube will start to get hot as it’s not able to flow through quick enough till it eventually reaches 110F inside the heater tube causing the OH code. Had a spa (Clearwater Spa) just today that uses a Laing circ pump and one (ozone) of the (3) 3/4" lines that return the heated water to to spa was plugged with calcium. One of the lines went to the waterfall and if you closed off the waterfall now they had 2 of the 3 lines not moving water. Kept sending a HLF code then a DR code and finally a dry code.

Sticky one way Valve or bypass valve not fully opening and creating problems.

 

[RDspaguy]

Is the water in the tub hotter than the set temperature?

Most OH errors are a high temp in the heater from low water flow. Remove filters. If it happens again, open the equipment area and touch the circulation pump. Is it hot, really hot, or OMG I need an icepack?

[contact634]

My 2001 altamar  did the same thing  in my case my recirc pump while running was not pushing enough water (20 years on a pump)  and the heater would hit over heat  I only found this problem as I had a spare recirc pump  installed it and never had an OH code again.....   might not be your problem

[HomePC]

Canadian Spa Tech: I put the model in the title of the post, but I should've put it in the OP also. Sorry. It is an 2001 Sundance 850 series Cameo. 240V, 1 high speed pump, 1 2-speed pump, circulation pump 24/7.  I don't have an accurate way to measure the temp; I am going to buy a pool thermometer later. I do believe the water feels warmer than the indicated display. I set the control panel temp down to 100 and today I had no OH error, but I thought the water seemed closer to 104. I'm thinking maybe the temp sensor is inaccurate and reading too low. I normally keep the control panel set at 102 or higher and if the temp sensor is off, it could cause the high limit sensor to kick in.

I just cleaned the filter and it's backup, though they are due for replacement. I'll keep the idea of pulling the filter in mind. Good advice. It never occurred to me that low flow through the heater could cause an issue. I have a Grundfos circulation pump, but whenever I get into the tub with the "OH" error on, the circ pump is working. Maybe weak? It also didn't occur to me that flow could be low enough to cause that "OH" error while being good enough to not cause a "FLO" error.

I keep all of the jets open and put the gate/slice valves into one position or another; never half way between. I have never had a scaling/calcium problem before, even while replacing motors/heater and parts in the access compartment; never notice any scaling/calcium buildup. I do fill the hot tub with softened water (water softener in the house) and keep an eye on the PH. I'll keep in mind that the heater could have buildup, but that will be the last thing to check as it is harder to access.

RDspaguy, contact634: I will try an keep an eye on that circ pump. It seems to put out as much as it ever did when I just sit in the tub with no main pumps running. But perhaps I have become accustomed to it over time.

 

Thanks for all the advice guys. After reading your replies, and having thought it might me an inaccurate reading from the temp sensor, I can see where low flow could actually be the problem, even after eliminating the error after setting the control panel temp down to a lower temperature. I think the first thing I will do is get an accurate reading on the water temperature with an external device. This should tell me if the culprit is the temp-sensor or low flow. Winter is setting in (Nebraska) and I'll see if I can limp into Spring; if the OH persists at that time, I will do more labor intensive diagnostics on it.

Again thanks.

Edited January 7, 2021 by HomePC
I have a Grundfos not a Laing

[RDspaguy]

The temp sensor, which you can see in the filter well, is prone to failure. The high limit (OH) sensor is in the heater thermowell with no direct contact with the water, and is far less likely to fail on a Sundance.

You can test the sensors with an ohm meter or mutimeter, but it is a bit of a PITA. Set temp low so that the heater is off and run it for 10 minutes to ensure no residual heat remains in the heater assembly. Turn off power and disconnect the sensor harness from the circuit board by pushing the two clips on the small sides outward away from the harness. Identify the two sensors and flow switch wires. TAKE A PIC OF THE HARNESS!!! There are 14 connection points in the harness with only 6 wires, and you don't want to put it back together wrong. Remove sensor wires from harness by inserting a small screwdriver into the slot on the side of the harness opposite the sensor wire to depress the retaining barb, then gently remove the wire. At this point, determine if you have the "box end" or "curled finger" type of sensor, as you will need to know which one to get. And, yes those are the technical terms used by Sundance.

If your meter is adjustable, set at 20k ohms, and take a resistance (ohm) reading on both sensors. They should be within a few hundred ohms of each other.

https://www.spaandpoolsource.com/sundancespastemperaturesensordiagnostic.aspx

It sounds alot worse than it is, and takes maybe 10 minutes to do. But it will show for certain if you have a bad sensor or another issue.

[HomePC]

More info. A cold spell came so I limped through the holidays and am back to readdressing this issue.  The OH error is happening more often now. Almost every other day the tub is shutting completely off.  If I turn off the 220vac breaker to the tub for 10 seconds, and flip it back on, the tub comes back up again and starts running, sometimes with the ICE or OH error displaying along with the temperature which never reads more than 105 on the panel and has been as low as 88 which would explain the ICE error. I've pulled the filter to help flow pressure. Didn't help. I am leaving the filter out while I do diagnostics.

I opened up the service bay today. While the OH was flashing with 103 degrees, I did a few things. I verified there is NO voltage to the heater. I didn't expect any but wanted to verify and make sure things are safe.  Second, I used a digital kitchen thermometer which was quick and easy. To my skin, I didn't think the temp was that warm, but the thermometer read 115 and I believe that is accurate. Photo attached.

I also did something else. I had an extra temp sensor (the one in the filter compartment) laying around from diagnosing a few problems I had in 2009. I verified it worked. The resistance measured was roughly around 36.49Kohms inside the house and the digital thermometer read 71.2, so it was pretty accurate to within a degree. I replaced the temp sensor in the hot tub with this extra one. Flipped the tub on and was still reading OH error, 103 degrees, and the digital therm was at 109 degrees after leaving the lid open and the tub off for about 20 minutes while I did the swap. I then measured the resistance of the old one I took off the tub inside the house and it read 37.94Kohms while the house temperature measured 72 degrees, so that is pretty accurate also, maybe off a few degrees.

Question: I thought the display temp came from the temp sensor in the filter well. If this is so, why does the tub temp read 103 while the actual temp was above 114?  I thought I read that was an indication of a bad temp sensor.

I do have an extra limit sensor (the one that goes with the heater) which I also tested in the house and seems pretty accurate. Should I replace the limit sensor that is currently in the tub with this extra one as my next move?

Edited January 4, 2021 by HomePC
Want to add: I've done all of this with the filter pulled to help flow pressure.

[HomePC]

New info. I noticed something else. When I flip the breaker back on, there is a gurgling noise in the heater. It settles down, then the 2-speed pump kicks on. I'm starting to doubt my circ pump. I tried resetting the tub a few times and also noticed a small whining noise coming from the circ pump. The circ pump is a Grundfos Pump Spa Circulating Pump, 59896292, 240Volt I put in November 2014. So, 6 years old. No FLO error. Flow switch is closed when running just on circ pump. I thought I had decent pressure inside the tub from the circ pump, but, like I said before, perhaps I've become used to a lower pressure over time.

 

[HomePC]

The more info the better, right guys. I turned the tub off, and pulled the sensor connector from the main board. My digital meter probes are fine enough that I could take ohm readings from the connector without having to pull out the box ends. Here's what I got.

Digital Therm in tub: 108

Display Therm on panel: 102 (No OH error at this time)

Temp sensor ohms reading (the one I just put in): 16.88Kohms which corresponds to about 102.5 according to the chart I have.

Hi-limit sensor ohms reading (the one on the heater): 19.09Kohms which corresponds to about 96.5 using the same chart.

Why is the hi-limit sensor so far off? I was expecting it to be sky high. I'll try and measure these sensors and tub again when I get the OH error.

Thanks for the help guys. Let me know what other info I can provide.

 

[HomePC]

Crawled in the tub this morning. Still feels great despite the problems I've been having. Display read "105".  Temp is set to "101".  Not sure it felt 105 but that could be me. Tub was on with no errors being displayed.  However, I could not feel the circ pump running. Normally I do, so it surprised me.  I'm pretty sure that is my problem. It may be running just enough to keep the flow switch closed or else the flow switch is shorted somehow.  Never have seen a "FLO" error. If I did I could think that maybe a relay was stuck closed, but i don't think so.  I think the circ pump is weak, causing water in the heater to rise in temperature, which eventually causes the "OH" error and the 2-speed pump to automatically kick on. Could that also cause the temp to get up to 105??? With all the sensors working (I think), I wouldn't expect it to hit 103 at the most before turning off power to the heater. ???

I still wonder why the digital kitchen meat thermometer read 115 yesterday. Maybe that was a bad reading or those can't be used to accurately read water temps. I'm pretty sure the temp sensor is accurate and yesterday I measured it's resistance which corresponded to what was on the display panel (103) even though the kitchen meat thermometer read 115.  I have an old-fashioned tub therm coming today that I can stick in there and let it float around. That should give me an accurate reading.

Repeated Question: is the displayed temperature coming from the temp sensor in the filter well or from the hi-limit sensor on the heater?

I'm going to order a circ pump today. Open to suggestions on good brands. Seems they all only last up to  7 years at the most.

[RDspaguy]

Wow. All of that and I'm still not sure.

For starters, the actual temp should read from the filter well sensor. It will heat water to 1 degree over set temp before turning off. Kitchen thermometers are not precisely accurate in my experience. 

Oh will trigger the pump to turn on, and low flow will cause the oh, as will several other issues. 

Grundfos are not as reliable as Laing circ pumps.

I'm hearing alot of assumptions about sensors, but not much real info. It does not need but a few hundred ohms difference on things reading tens of thousands of ohms to have a sensor mess things up. The board can also sometimes be calibrated, so can go out of calibration over time. A calibration issue effects both sensors equally, but could explain your set temperature issue.

I would recommend, without being there myself to test it, that you replace the circ pump and sensors. Sensors are prone to failure and that circ pump just looks like it needs to be replaced. If it is still not reading accurately we can see about calibration. 

Post a pic of your circuit board.

[HomePC]

Thanks RDspaguy

Been thinking about this. The low 95 degree reading I got when testing the ohms on the hi-limit sensor could've been an accurate reading, if the water was just sitting in the heater housing cooling off faster than the water in the insulated tub, if the circ pump wasn't pushing water through it.  I never ran the pumps for a few minutes to get water flow through the heater before I measured that sensor. My bad on that one.

Still wonder why the display read 105 when set temp is 101. I'll keep in mind that maybe this board can be calibrated:  850 circuit board with 1.28k eprom Board: 6600-056, Eprom: 6660-322

I have had two Laing pumps earlier, but they also failed around 7-9 years, but could've been due to two Sundance plastic heater housings developing a small hole (same location too) and dripping on the circ pump causing premature failure. I have since moved the circ pump to a better location. The old 2001 Cameo had it directly under the heater. I am also using the stainless steel heater model now. Here's the link if anyone is interested (they seem to be harder to find today):

 https://pool-spa-supplies.com/therm-products-spa-heater-5-5kw-240v-lo-flo-13-x-3-vertical-with-box-e2550-3314-15735

I attached a pic of one of the old Sundance heaters (model 6500-310) so anyone interested can see where the hole develops. Right where the hi-limit sensor goes into the housing. I keep all of my old parts, which is why I had extra sensors lying around. (-;

I'll probably get whatever has a better price for a circ pump. Might even look into generic ones if they exist. Expecting a pool thermometer tomorrow from Amazon. That will help with more accurate readings from the tub. I'm not trusting that digital kitchen meat thermometer either.

p.s. Just went and checked on the tub. Temp is set to 101, display reads 101, and the circ pump seems to be working at the moment. I increased the set temp and saw the heater kick in, no OH error, no 2-speed pump kicking on. Circ pump seems to be working at the moment. I think it is just flaky.

[RDspaguy]

I'd trust the kitchen thermometer over a pool thermometer any day.

[HomePC]

13 hours ago, RDspaguy said:

I'd trust the kitchen thermometer over a pool thermometer any day.

I tested the calibration on that Taylor therm in boiling water. It sat at 212 degrees just as it should.  So now I'm confused on why the set temp, temp sensor, and Taylor readings are jumping all over the place, before and after replacing the temp sensor (used sensor). Last night the set temp was 101, the display temp was 101 and the circ pump seemed to be running. This morning the set temp is 101, the display temp is 103, the Taylor measured temp is 109 and I have the "OH" error.  I ordered a new circ pump. In the meantime, I can program the 2-speed pump to run continuously for a few days. Maybe that will give us some new info.

Is it possible both the temp-sensors I used are bad? The display temp is staying close to the set temp despite the actual temp. Could board calibration have anything to do with this?

I should point out that I disconnected the air pump a couple of years back. It was causing the breaker to trip. I didn't realize until now that it is also used in cooling down the tub.  Guess I will replace that too.

[HomePC]

Rereading any literature I have on my tub. Ran across this about "Summer Logic". Wondering if this could also cause an "OH" error in my case and maybe why I sometimes don't see the circ pump running.

"Summer Logic: In warm weather, the water temperature in the hot tub may
exceed the set temperature. This condition may occur due to heat transference
from the main pump and 24-hour circulation pump. If the water temperature
is higher than 95°F (35°C) and rises two degrees above the set
temperature, a “Summer Logic” condition occurs that deactivates the circulation
pump and ozonator (if equipped). This safety feature cannot be
altered! The circulation pump and ozonator will remain off until the water
temperature cools to the set temperature (except between12AM-2AM when
the circulation pumps runs for it’s mandatory 2-hour “clean-up” cycle). To
help prevent a “Summer Logic” condition, it may be necessary to reduce
skimming/heating cycle and/or circulation pump run times in warm
weather."

So, a slightly high temp sensor reading over the set temp will cause all pumps to shut down, but an "OH" error caused by the high-limit sensor causes the 2-speed pump to turn on. I guess the designers assume an "OH" error can occur while the water temp is within the set temp range. Interesting. I guess I can understand the logic to that.

Got my spa thermometer today. It is reading the same as the set temp.  I wonder if the kitchen digital therm isn't accurate at lower temp ranges. I'm testing it in ice water and can't get it below 39 degrees.

[HomePC]

I have programmed the circ pump from 24/7 to 0/0 so it won't run programmatically. The 2-speed pump is already programmed to run at 6am, 12pm, 6pm, 12am for 30 minutes at each time. I turned that down to 15 minutes. If the water temp drops below the set temp, the heater/circ pump are suppose to kick in to heat the tub back up. If the water temp drops more than 20 degrees below the set temp, the low speed pump is also suppose to kick in. So I shouldn't have to worry about it freezing.

My thinking is there may be heat transfer from the equipment bay to the heater housing causing that OH error. I haven't had the breaker trip in quite a few days too. Not sure why not when it was tripping every few days. 

I may disconnect the secondary control panel in case it has water or something in it causing a motor to kick on/off randomly. Again, thinking a motor might be heating up. Might even try 'economy' mode so that the filtration cycles are turned off. The heater/circ pump/low-spd pump should still work as above.

Ordered a circ pump. Won't get it for a couple of weeks.

[HomePC]

New day. I'll keep adding what I can to this post in case someone is following it. Set temp is 101, display temp is 100, no pumps are running. As expected. I went back inside the house and after a short period (maybe 15 minutes or so) I heard the low-speed pump kick on when it shouldn't have.  I went out and checked the display and sure enough, it has an "OH" error. The water temp must have dropped another degree causing the heater and circ pump to run (the circ pump is suppose to run when the heater kicks on despite having programmed it from 24/7 to 0/0).  I guess the flow was not enough causing the "OH" error from the hi-limit sensor in the heater unit which also causes the low-speed pump (and air blower if I still had one) to kick on to help cool the tub (or in this case the heater housing) down. 99% sure the circ pump is the problem though a faulty hi-limit sensor may still cause these symptoms.  A buildup in the heater (calcium/corrosion/etc..) could maybe complicate the issue as mentioned above.

[RDspaguy]

On 1/5/2021 at 12:55 PM, RDspaguy said:

would recommend, without being there myself to test it, that you replace the circ pump and sensors. Sensors are prone to failure and that circ pump just looks like it needs to be replaced. If it is still not reading accurately we can see about calibration. 

Post a pic of your circuit board.

 

[HomePC]

Yup. That's what I am doing. I'm also trying to establish a pattern as to what is happening to help others who might catch this post in the future. Help them try to narrow things down based on their symptoms and by eliminating variables. I'm going to replace the hi-limit sensor in the next few days when I get a decent day, since the circ pump won't be here for a couple of weeks.  What other testing would you do that I haven't already done?

Regarding a digital thermometer, I found out that some cheaper ones are better calibrated to a certain range of temps and give inaccurate readings outside that range. In my case, I'll stick with my glass-tube thermometer which is reading the same as the display.

[HomePC]

Think I've found the problem. With the set temp down to 100 the display panel was reading 106 along with an "OH" error. I had already replaced the temp sensor so I thought it might be heat transference from a motor running hot and was worried it might be an expensive main pump. With the set temp at 100, the water temp at 106, I turned off the breaker, waited a good 10 minutes to gather my tools and opened up the equipment bay.

I double checked all 3 sensors. The flow switch was open when the tub was off and later when I turned the tub back on the flow switch was closed with the 2-speed pump on or when only the circ pump was working, so the circ pump is working at least well enough to close the flow switch. The temp sensors I measured immediately after initially turning the breaker off. Temp sensor measured 15.82kohms (which should be around 105-106 degrees) and the hi-limit sensor measured 13.90kohms which is off the chart but probably above 110 degrees. The lower the resistance the higher the temperature with these sensors. My chart only goes up to 16.149kohms which is 104 degrees.

When I turned on the breaker, I heard the "gurgling" sound in the heater that I mentioned in an earlier post, and measured 240v going to the heater until the "OH" error started (maybe 30 seconds later, not sure on that time) which turned the heater back off.  The display panel did NOT show that the heater was running. The temp sensor should have been keeping the heater from turning on.

After running the tub for a while, I checked by touch for heat from the main and circ pumps.  Not hot to the touch at all.
I went ahead and put in my other hi-limit sensor anyway, since I had the equipment bay opened up. I believe all 4 of my sensors (2 hi-limit / 2 temp) are good.

I figured I had a stuck relay on the main board, in particular, the one that goes with the temp sensor. I turned the tub off again, took my hammer and gently tapped on all of the relays, turned the tub back on, and no more 240v to the heater and no more "OH" error.

I think my 20 year old board is needing some attention. I'm good at soldering, if I can limp into Spring maybe I can try to find new relays and solder them on the board. I read somewhere that somebody attempted that. Hate to buy a replacement board. Expensive.

I also wonder if my old circ pump is too weak for proper water flow through the heater to prevent the "OH" error even with a stuck relay. But when the heater is heating water that is already at 106 degrees maybe it might still cause the "OH" error????? . Anyone know what the high-limit temp is on these 850 LCD boards? I did receive a new circ pump yesterday (I thought it was going to be another few weeks). I'm going to let things run as they are for a little bit. See what problems pop up. MIght be a good idea to replace that old circ pump anyway; I thought it was acting up.

Does my analysis sound correct to everyone????

I've attached a picture of the main board.

[RDspaguy]

Typically a spa will display an oh if any sensor reads above 108 to 112 degrees. The temp sensor reading the wrong temp is either the sensor or board. Just because you have 2 used sensors does not mean either is good. I have had brand new sensors that were bad on several occasions over the last 26 years. If the resistance reading shows a temperature per the chart other than what the actual temp is, you have a bad sensor, period. If the resistance matches the temp but the display does not, you have a board issue.

The gurgling sound you hear is likely water boiling inside the heater, which is the result of low or no flow. A stuck relay will engage the heater before the circ pump turns on, which will cause it to boil. A faulty circ pump can cause the exact same issue even when working well enough to close the flow switch. The flow switch itself can fail and give a false closed reading too, but this will usually cause a flo error.

I would recommend a professional electronics repair shop for the relay replacement, you only get one chance to screw it up and then you are buying a new board.

On the left of the board above the heater relays is a white sticker. Above the sticker is a discoloration on a circuit and one side of a resistor, right beside the heat sink. Is that a burn?

[HomePC]

The temp sensor resistance, the display temp, and the actual temp measured with a thermometer are all the same.  Also, the resistance measured on the hi-limit sensor puts it in a range that would trigger an "OH" error on this tub.  There is nothing wrong with the sensors. They are doing their job (thankfully for the high-limit sensor).

I agree there may still be a flow problem as indicated by the boiling water in the heater.  Even though the heater should not have been on, the circ pump should have put some flow through it to keep it from boiling; at least I would think.

I am an electronics engineer. B.S. in Electronics Engineering Technology. I've designed and built circuit boards in the past. I've done computer board work for people also. Working on the board shouldn't be a problem if that is the route I need to go.

If you're referring to above the Revision sticker, I think that is a reflection, but I will inspect it closer in the daylight tomorrow. Good catch. I did inspect the board and that didn't catch my eye.

The OH range of 108-112 was something I was trying to find out. I thought it might be more like 114-120 before the "OH" occurred. If the tub keeps heating until the temp in the heater reaches 108 or so, I guess the water temp in the tub would probably be a few degrees cooler than in the heater. Seems to jive with what I have been experiencing.

Thanks for the input.

 

 

 

 

[RDspaguy]

So you are the electronics pro. Perfect. 👍

Of the three heater relays, 2 are switched by the high limit, and turn on as soon as the breaker is turned on as long as the heater temp is below 112 or whatever. The thermostat relay is the switch that turns it on and off during normal use, and is the one that wears and sticks. I often recommend replacing all three to be on the safe side, but you likely only need the thermostat relay.

[HomePC]

So far the tub is running as it should since lightly rapping on the relays. No "OH" errors.

I was scouring the Internet yesterday trying to find a good schematic of the board. Can't find one that shows the interconnection between the switches, relays, and mechanical devices. The switches probably lead to the eeprom where programming will determine whether to trigger a relay or not.  If I get to the point of pulling the board I can trace the etching lines on the back. But, just from looking at the relays on the front, K1-K2-K3 go to the heater, K4-K5 goes to the 2-speed pump, K6 goes to the 1 speed pump, K7 goes to the circulation pump, and K8 goes to the ozonator which I have disconnected. K9-K10-K11-K12 not sure about but one of them probably goes to the air pump.  Again, just guessing.

Have not put in the new circ pump. Debating on that. It is a nice thought to think I have a brand new, extra circ pump sitting on the shelf if I should need it down the road. On the other hand, if I don't put it in, I can't verify it works within the warranty period. I know I said I thought the old circ pump wasn't running all the time, but after reading about the "Summer Logic" , which I quoted above and have reposted below, that could be normal. I'm guessing my circ pump was turning off between the when 2 degrees over was reached, but turning back on (maybe) when the "OH" error occurred. This probably compounded my problem since the heater relay was stuck closed. Could explain the "gurgling" sound in the heater housing too. Turn on breaker, water temp is a few degrees above set temp but below OH temp, so circ pump is off by "Summer Logic", but heater relay is stuck closed causing heater to heat with no flow through it until the "OH" occurs and the low-speed pump (and maybe the circ pump) turn on.

NOTE: After a long filter cycle, you may notice that the water temperature
is greater than the temperature setting. This can happen in such a well
insulated hot tub because, even though the heater turns off as intended,
the transference of heat from the pump continues to add warmth to the
water. If the water temperature is above 95°F (35°C) and two degrees
above your set temperature, the circulation pump (and ozone generator, if
equipped) will shut off until the water temperature cools to the set temperature.
In warm weather, it may be necessary to reduce filter cycle run
time to prevent this type of heat overrange from occuring.

This may be my last post unless things change. For now, all is good. I appreciate the help.

EDIT: 9-30-2021, wanted to add that I did install a new circulation pump. Did not solve the problem. The old one was going on 10 years, so I probably needed the new pump anyway. I can live with that cost.

Edited September 30, 2021 by HomePC
Installed new circ pump:

[HomePC]

Wanted to finish this post up for anyone else who runs across it.   I limped through the rest of Winter with the "OH" error. During the Spring and Summer I left the tub off days at a time and turned it on a few hours before evenings that I thought I would use it; then I would turn it back off. I just didn't like the idea of the heater running constantly until it hit the high-limit (OH). I could tap the 3 heater relays and the voltage to the heater would go off, but once the temp of the tub dropped and the heater kicked back on, it would stay on. PITA.

REMINDER: this is a Sundance 2001 850 Series Cameo "CONTROLLER 850LCD" circuit board.

At any case, today, I did pull the circuit board, removed the three big relays (Zettler AZ2100-1A-12DEF) that fed the heater. They were labled as K1, K2, and K3 on the circuit board. I soldered on 3 new relays I got off of Amazon. Works perfectly. I think it was the middle relay K2 hat was having issues. I replaced them all. K1 and K2 fed the heater's RED wire while K3 fed the heater's BLACK wire.

I did follow the trace lines to see what the other relays went to. The five Potter & Brumfield T9AS1D12-12 relays were grouped as two separate groups. The 3 in a group labled as K4, K5, and K6 went to the 3-wire  2-speed pump (TB1). The 2 in a group labled as K7 and K8 went to the 2-wire 1-speed pump (also TB1).

If memory serves me correct, the four Potter & Brumfield relays RKS-1DG-12, the two outside ones labeled as K11 and K12 went to the circulation pump (TB2), the inside two labeled as K9 and K10 went to the ozonator (TB6) (which I don't have). 

The blower (TB4) did not have a relay associated with it. It may run through the circuit board fuses. There are 8A and 15A fuses on there which should suffice for a small blower motor.

On my tub, TB5 is the SPA light, and TB3 is not used.

Hope this helps someone.