Hey all. Looking for some direction to fix my hot tub problem . I have a 20 year old tub with a Spa Builders LX -15 spa pack (revision 7.51 sticker on the EPROM). The motor and pressure switch have been replaced; but I believe temp sensors are from the original build.
When heating the spa and the temp reaches 97 degree; the bubbler ( to cool the water) comes on. The heater stays on and there are no error codes generated. This will keep happening several times (after turning off the bubbler) ; until the water is at 97 or 98, and then it typically won't happen again. Also, in a possible related issue; the water won't heat to 104. The bubblers come on, the heater turns off and I get an OH code at cooler and cooler temps (down to 99 degrees) (this problem appears progressively worsening in that, over time, the spa is reading OH at cooler and cooler temps).
I have checked the water and hi temp sensor; they both read similar ohms and appear to have the correct resistance (per the spa builders trouble shooting guide) and the water temp of the spa on the top side correlates with a thermometer in the water.
Otherwise the spa works well with no other error codes. The ozonator with the spa no longer works dating back years ago.
I''m thinking I need to replace the circuit board; it just seems like an odd way for the logic system to fail. Thanks for any insight. Circuit board and circuit diagram pictures attached.