Need Help with Hi Limit Issue - Barefoot MR88

[AdamB]

Hi guys, I need some serious professional help! I have a Barefoot MR88 spa, built in 2005. Within the last year I have had to replace the circulation pump on it (which I did myself) due to flow issues which were causing the Hot Tub to not heat. The Tub worked well for about 6 months and now has decided to have problems again. What happens is the Hot Tub will only heat water for roughly 12-24 hours after a power cycle and then I will get a 3 dot error code (which I have traced to be a Hi Limit issue). I should note now that flow in the tub seems fine, I get decent pressure out of both circulation discharges.

My initial thought was a flow sensor issue after research so I replaced the pressure switch. This didn't fix the issue. So I opened up the Spa Pack and I see a red light listed as Hi Limit lit up in the upper right hand corner of my spa pack. I have read there should be a reset for this, but I can't find one on my unit. My unit is a circuit board unit so maybe there shouldn't be one? A Power Cycle (shutting off the breaker at the GFI for 1 minute) will turn the Hi Limit light off and allow normal usage for a brief amount of time. After about 12-24 hours I will return to find the tub with the 3 dot error code again on the display. The Hot Tub will definitely heat fine, I was able to heat the water from about 85 to a set temp of 98 without getting an error.

My last test I heated the water up and upon reaching set point (and still not having a Hi Limit error) I actually turned the temperature way down (about 10-15 degrees) to ensure the heater would not engage. When I did so my circulation pump also shut off, I assume this is normal. I came back a few hours later to still find the Tub had thrown a Hi Limit error, even though I assume between the time I left it and the time I came back the heater nor the circ pump ever turned on. It had only lost a couple degrees obviously so was still well below the set point, but had the 3 dot error code.

Some additional Misc info that may be pertinent:

• I did once notice when going through a power cycle that the digits on the display were blinking upon turning the tub on. The manual says this denotes a very high temperature, but the blinking temp was only in 80's.
• My tub has 3 pump zones (not including the dedicated circ pump), one of which broke down long ago and then a while back sprang a small leak at the pump so I have since closed the gate valves on the pump so as not to have to mess with fixing the leak.
• After I replaced the circ pump I did notice quite a bit more bubbles coming out of the circulation discharges in the tub. They aren't big burping bubbles, more like smaller champaign-like bubbles. I have no idea where the air is coming from and if this is intended or not or if it could have any effect on the heating system.

I appreciate any help you all can give me and would be happy to further diagnose in whatever way you guys need for more information. I am pretty handy and do have a multimeter at the ready.

[AdamB]

Guys, I did a little more diagnosing and have discovered that the Hot tub heater is not turning off as it should. When the set temp is reached the circulation pump shuts down, but the heater stays on. I discovered this by removing the Hi Limit probe from the heating tube, I came back some hours later to find the Hot Tub hadn't tripped a Hi Limit error and the Heat Tube was VERY hot. I could barely touch it, surely higher than 120 prob, glad I didn't leave it like that overnight. I am sure it would have tripped if the sensor were in place.

So I am guessing that the Hi Limit sensor and circuitry is doing exactly what it should, shutting the tub down when it gets too hot in the heat well. The real question now is why is the heater being fed power from the board when set temp is already reached and the circulation pump is off? I also discovered I have a Gecko MP board.

Can anyone tell me what type of heater I have from the linked picture? https://photos.app.goo.gl/53y4n7q4iRSXxVjw9

[AdamB]

More research, one possibility is a stuck heater relay on the board apparently? Does anyone have any experience or knowledge with this that could help me diagnose this further and figure out if this is indeed the case and if so how to fix. Even if it involves taking the board out of the tub and taking it to a local small electronics shop so they can put a new relay in, that's way better than footing $300+ on a new board. I would likely need to point the shop to the culprit relay though and probably have the relay on hand for them to replace.

Here is another link to some photos I took of the board if you guys could help. https://photos.app.goo.gl/yMUQfbptHT9aVy5T7

[Jacuzzi Jim]

  I would replace the temp sensor if anything at this point.  Its a cheap part and will do what you are describing. Hi limits are cheap as well.    Not sure you can replace just the relay on a Gecko board or not?

 

[AdamB]

I had thought about temp sensor, but if that was the case wouldn't the topside display not be showing the correct temp? Topside display shows temperature correctly as best as I can surmise. And the circ pump seems to be behaving as is should in relation to set temp, meaning when set temp is higher than actual water temp it turns on and when set temp is lower it turns off which again leads me to believe the board is getting a proper current water temp. Thoughts?

I assume as far as the relay and board goes it's all circuitry so the feasibility of replacing the relay really just comes down to the ability to safely extract the board from the tub and secure a proper relay replacement (may be the hard part). After that it's jus desolder the old relay and resolder a new one which I wouldn't do, I'd let a circuit board tech handle.

[AdamB]

I think I am pretty close to figuring this out, but want to keep posting so if anyone else has this issue it will be well documented on here.

More Diagnosing:

So I opened it up all the way down to the circuit board and got out my multimeter and here is what I find. When the hot tub is on and heating, I turn the Hot Tub "OFF" at the top side control panel I can distinctly hear first the heater relay click OPEN (as it should) and then in about 10 seconds I hear the pump relay click OPEN, makes sense. When I turn the hot tub back on I hear the clicks again in the reverse order, pump being brought online followed by heater, again all good.

I then wanted to test voltage across my 240V heater when the tub is actually calling for heat and when it isn't and that is where things got interesting, here are my results:

Tub calling for heat:
Across heater terminals/legs (white and black) I get ~240 Volts and from each heater leg to the main ground or Neutral I get 120V. From research this is what should happen, it tells me the heater is running, which I already know.

Tub set to "OFF":  (I would assume board should cut basically all functions of the Hot Tub, definitely the heat)
Across heater terminals/legs (white and black) I get ~6 Volts which slowly creeps upwards to about 9ish Volts over 3-4 minutes (BAD)
From White heater leg to ground and neutral I get ~120 V (What is expected)
From Black heater leg to ground and neutral I get ~112V (I am not big into electricals but I assume the missing 8V is what I am seeing when measuring between the legs)

What I derive from all of the above is that even when the board thinks it has turned the heater off about 8v is leaking through to the heater which is slowly heating the water in the heat well. This inevitably trips the Hi Limit (albeit slowly as the 240V heater is only heating at roughly 8V). I can verify that the heater is still producing a small amount of heat over time as after about 5-10 minutes of the tub being in the OFF state, the heat well is getting rather hot.

Lastly, I actually dipped the Hi Limit probe in a cup of very hot water and observed a safety trip while the tub was in the "OFF" condition. Upon tripping, voltage across heater legs went from ~9V to 0V, which is where it should have been all along once the tub stopped calling for heat.

My best guess at repair, and please I really want feedback, is that the heater relay is possibly a bit corroded or weak and even when it clicks OPEN there is still some minor connection allowing voltage to slip through it. I am not well versed in electrical circuitry though, so this is all a hypothesis, would love someone with REAL knowledge to step in and let me know I got it and I should rip the board out and replace the relay. If there is another board defect to pinpoint other than the relay which is letting the voltage slip through to the heater I would love to know.

It will take probably about an hour of time, $5-10 for the relay and another $30-50 to have the relay replaced, but that is nothing if it actually fixes the problem.

[Jacuzzi Jim]

When a temp sensor typically goes bad, it either will show the normal temp but the spa will be cold.  Or it will show the normal temp but the spa will get really hot and eventually the HL trips the breaker.     My Jacuzzi did this a few months ago, temp read 101, water was actually 111 and probably close to tripping the HL.       

    My guess is the temp sensor is fooling the board so it's still sending power to the heater when not calling for heat.  If that makes sense?     If the spa is not calling for heat via the controls there should be no voltage at all.    Though you say when touching the legs separately your still getting 112 and 120v?

 
 Not sure that leaking 9v are going to heat the spa high enough to trip the HL.