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Help! Troubleshooting Hot Tub

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Hello! I'm new to this forum, and am praying someone can help me out here....

I have a 2001 Marquis Ultimate Series hot tub that is exhibiting some OH and OHH overheating codes that I'm having some trouble diagnosing... First a bit of history:

Two months ago (Nov '11) I was getting an overheating shutdown condition and I troubleshot it to my primary pump having been stuck in the high-speed cycle during filtering which caused the original overheat condition... I replaced the pump and while I replaced the pump I figured I was on borrowed time with a 10 year old heater so I replaced the heater as well with another Balboa (Marquis P/N: MRQ740-0617..) 15 inch heater before winter set in... Everything worked great... until two months later... Bear in mind the temp sensors are part of the heater element (1 "upstream" of the heater measuring water temp inflow and 1 "downstream" of the heater measuring water temp outflow--my Marquis model only uses those temp sensors as I don't have a probe in the tub basin or anything like that)... So essentially I have new temp sensors as well as the heating element itself.

Also, my panel settings are as follows:

FC3 (3 hour filter cycle)

1C (1 cycle per day)

SL1 (1 hour smart cycle after the tub gets used)

Temp setting 102F

I changed the water and both filters in November when I swapped the pump and heater out and they are both clean

And I have an ozonator

This past Friday, I opened my tub after not using it for a few days (with ambient air around 15deg F) and noticed the water was cooled down to 91F (from a requested setting of 102F on my panel) and the top panel denoted an OHH code... The LCD temp was verified with a floating thermostat I have floating in the tub for reference. I turned the pumps back on via the 3 zoned control stations and everything kicked back on... The heater turned on and I ended up having to go to bed (as it would've been pretty late staying up late to monitor) and I returned to it in the morning and I got an OHH code to welcome me... So now it stayed in the OHH mode all day, despite flipping the GFCI switch off and on until the afternoon when it came on... I went out for two hours and returned to find it overheated again. It stayed that way until the evening time when the tub finally responded (and the LCD Temp matched the floating thermometer of 102F)... After priming and initially searching for a temp reading (which it accurately gave as 102Deg F), it ran... after the 15mins passed associated with when I actuated zones 1, 2, and 3 (which activate the jets for 10mins high cycle and then a 5 min low cycle) the primary pump switched to a low-cycle filtering cycle (as the tub was automatically set to filter upon power-up... Which I assume it would immediately transition to do despite me actuating the high speed jets at start up...) Now this is where it gets weird... It was approx 17deg F out last night and I had the entire tub open and exposed to the ambient air... The heater light was OFF, and the primary pump was pumping in the low cycle filtering and the temp in my tub was climbing fairly rapidly.. It climbed from 102 up to 106 in about 30-45mins with the COVER OFF THE TUB in 17deg F weather and NO Heater light on! Only the primary pump cycling low speed... by this time it was getting late so I flipped the fuse when the LCD panel read 106F and tub running and went to bed....

I woke up this morning (around 20deg F), flipped the GFCI switch and waited for the pumps to prime... Immediately after priming, the panel flashed the OHH code (without even doing a temp cycle check)... The floating thermometer showed the water temp dropped to 97deg F... Now.. when I went to bed I flipped the power off while the tub was NOT in an OHH state... Its 17-20deg F outside over night with no power to the tub, I flip the power on (with the tub water at 97F) and immediately get an OHH state!!! AHHHHHHHH!!! I had to wait two hours before the tub would respond with an initial water temp check (where it flashed OHH again...).. I had to wait again, however this time the tub powered up and began a one minute water temp cycle, while I had the one minute to access my LCD panel, i switched my filter cycle to 1N which denotes one cycle per day, 12 hours AFTER power is turned on... this time the tub has behaved normally... It heated up to 102F and shut off... I actuated a 15 min jet cycle (10 at high and 5 at low) and it responded normally... The tub is now idle...

So this leads me to the following observations:

1.) I'm suspecting that somehow, despite a new heater and pump, despite my primary pump running a reasonable/standard low filter cycle it seems to be heating my tub pretty rapidly (i.e. no heater light coming on)! Again, I'm not over filtering my water to have my primary pump on for THAT long...

2.) The top panel LCD temp matches another thermometer I have in my tub

3.) Could I have a bad inlet temperature sensor on my brand new heater? If so, how can I check? But that still wouldn't explain why the water is heating the way it is

4.) My heater appears to turn on and off when needed

5.) I can't explain why my tub would give me an OHH in the morning after it sat POWERLESS overnight and the power was shutoff last night at a temp reading of 106F....


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