Score one for me.
See how much you've learned over the years!! We're all soo proud!!
We see it happen more frequently in the winter at a water change. We were told by Lasco, a maker of plastic unions, that the cold water going into the tub and the plastic being warm can cause them to losen up because the exspansion/contaction of the plastic.
Lasco makes the union? They usually make the fittings that lead up to the union however the union itself is usually made by someone else.
I would think that Blue Falls Manufacturing (plastics division) would make those considering they are the parent to Arctic.
Tom,
Can you verify this?
All spas deal with warm water...excusing it with hot and cold is not a good thing. They need to get to the bottom of it and find a solution. Like I said, several manufactures put a dab of silicon on the threads to keep them from loosening.
I would also think you would have more expansion and contraction from the heater tube itself.