Peteyboy

If it was airlock you would hear the pump running. If it's not running check the 2 Buss fuses in the middle of the circuit board.

If no one mentioned it be sure to notch the metal bracket so it doesn't touch the optocoupler.

Sounds like you have a HotSpring spa having the 2 breakers. The smaller HotSpring spas use the 30 amp breaker to power the heater. You may have a bad heater.

Some had removable panels. If you feel 2 notches under the lip and 2 or 3 angle brackets it should be removable. If not you have to pull off the slats...fun.

If it's a Grandee I hope you don't just plug it in. You should have 2 separate GFCI breakers for that spa.

If you are in a warm climate the HotSpring spas hold the heat very well. Put a rolled up wash cloth under the edge of the cover to let it breath.

I wouldn't add ozone to the TX unless you retro it to a circulation pump system. You would have to run the spa too long for the ozone to be effective.

The ready light also has about a 5.5 degree window. It doesn't stay on if you lower the temp way down.

If you don't have new o-rings plug it with your finger and be quick. Turn off power before doing it.

That is probably an air intake with a rubber flap that has failed. You can re-plumb it or seal it up with silicone and not have air into the jets.

The easy way is to drain the spa and remove components that are in the way. You can plug the 3/4" hoses with wine corks or C size batteries.

220V conversion only powers the heater 220V. Like djski said, the spa will not heat with the jet pump running if connected 110V. In a very cold climate I would convert to 220 so it will heat with the jets.

Check power at the heater terminals on the heater relay board. If you have power there it should be a bad heater. If no pwer there check power at the wires from the heater relay board to the main board. It could be a main board problem. I'm not on here much so I may not respond again.

Is there a GFCI on the cord? If so, even if it lights up it might not be sending power to the spa. (If there is no GFCI I hope it's plugging into one or the breaker for the circuit is GFCI, Don't use the spa if there isn't one)) It's possible it's just a bad GFCI. If not you need to pull out the control box and troubleshoot further.

If the spa is heating fine and the red light flashes even with the filter out then I would replace the high limit thermister. They are pretty cheap. Good Luck