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Need Help with Hi Limit Issue - Barefoot MR88

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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.

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