Spa Board Doctor

Green "LIMIT OK" LED is for the high limit. You mentioned that you spliced the wires for the high limit and the temperature sensor. You'll want to check to see that these connections are solid. I always use solder and heatshrink to splice. If it's not a bad sensor connection, then there may be a high limit condition occuring from low water flow i.e. restricted filter, obstruction in the front of the circulation pump, or intake/plumbing/return restriction.

Make sure the temperature is set above the current water temperature. Are there any error codes on the display?

Is the "LIMIT OK" green LED lit?

Not sure. I guess wiggle things around and see if something stops/starts. 😏

Post a picture of your circuit boards.

If the green "LIMIT OK" LED and the red "HTR ON" LED are lit on the main board, test across the two heater legs on the heater board. If the hot tub is 240V there should be 240VAC across these two (If 120V then 120VAC). If the voltage is not present then there is either a bad relay, blown trace, or if the board is newer (green/red LEDs on heater board), it may have a circuitry failure. All of the above are repairable failures.

It's most likely that the green is still the ground and the other colors are the line wires. The line wires don't have polarity i.e. they can be hooked up, one each, to either of the connection points.

It sounds like the relay for the heater is sticking on sometimes. This is a repariable failure.

Nice work! There's nothing quite like a mis-engineered lo-flo heater system. The restricted flow across the heater causes the dissolved calcuim and magnesium in the water to precipitate and crystalize into scale. One thing that helps is to lower the wattage of the heater to 4kW. When I replumb tubs that have failed lo-flo heater designs, I use four 3/4" returns. Two ozone jets with the nozzles removed and air lines plugged, one ozone jet with the nozzle installed (use this one for the ozonator), and one 3/4" straight bulkhead return fitting. This combination provides adequate water flow for the heater and enough back pressure for the venturi effect on the ozone jet with the nozzle left in.

Is the water temperature very low? If the temp is below 44F, "ice mode" will turn pumps on to high speed until the water warms up a little.

For the scum line after the spa flush, a "Magic Eraser" works amazing.

In test mode, you can see the values of the two sensors in real time. If the value of one sensor rises to more than 4 degrees F higher (assuming the earlier input voltage detection circuit hasn't been repaired) than the other, the computer will throw a "dr" code. If the voltage detection circuit is repaired, the delta between the sensors to throw the "dr" code would be 6F. Either way, if one sensor climbs 4-6F higher than the other, it is an indication of a water flow problem, not a board issue.

Have you run it in test mode to see the A/B delta?

It can be, but I've also seen other components in the circuit fail, like resistors, and a triac. I have to use an oscilloscope to figure it out.

It is possible that the temp up button on the keypad is stuck on, causing the setpoint temperature to be displayed at max, 104F.