We have a ‘92 or ’93 Dimension One President hot tub with a Balboa 27600 controller board which is giving me fits. A little further description: single speed pump, no blower. I removed the ozonator and installed an air pump from an old pneumatic hospital bed mattress in its place…works fine, circulates the water well enough to heat and keep the flow switch activated. Our problem is that it overheats. It had worked fine for months after I hooked up my odd " title="Laughing" /> air pump when the ozonator air pumps died, and then one day I noticed it was getting hot. I lowered the temp setting on the upper controller and it continued to heat. It would not stop heating up, no matter how low I set the temp. I cut the power when it went above 112 degrees and it was set at 80. I checked the resistance readings on the sensor harness and both sensors were in the ballpark of what they should read in KOhms (I got a chart from a source that I found on the internet when I was trying to get a schematic from Balboa) given the water temp. (Does the sensor that inserts in the heater block actually do anything?) I took the Balboa 27600 board out and looked it over (I’m an electronics tech). No leaking or bulging caps, the relays were not stuck, all board fuses were good…nothing obvious that I could see, and without a schematic and test point readings I was basically looking for something that would stand out. I put the board back in and powered it up. Same thing, but I noticed that the heater indicator light on the upper control panel correctly follows the temp setting. That is to say, when I set the temp at 95, and the water temp is 95, I can increase the temp setting on the panel and the heater light will come on and I hear the relay click. It takes a couple of days for it to overheat, from 80 degrees to 110 (where I removed the power to the system), which is way longer than it normally takes when I refill it and want to get it up to temp. So something is causing the heaters to kick on at certain intervals, but not continuously. And I’m not familiar with any possible calibration pot on the board, or so-called “summer setting” (had the house for four years and never had to address any kind of summer setting). Upper controller or maybe the control board? I would think if it were the sensors, I would see an open, no? I’m kinda puzzled and would appreciate assistance. Thanks. P.S. D1 seems to no longer sell any electronic parts for my model, so does your shop carry such parts that I might need?