I have a 1995 Polynesian tub. It WAS working fine, but now has a heating issue.
I replaced the heating unit, with a brand new one (120V, 1KW, Balboa heater), but still only 90 Deg. The relay that activates the element IS energized, so 120V is going to the element.
I disconnected the high limit switch to make sure it is working correctly, it is.
The light on the thermostat does turn on when the relay pulls in, so I think everyhting is OK in that department.
[b]I AM CONFUSED!![/b] Any other ideas?

I would check voltage at the heating element terminals. If you have power there, then you have an issue with insulation, where your tub is loosing heat as fast as it is being heated. If this is the case, look into a better cover, more insulation around the surround, and definentally, put some pink styrofoam insulation under the tub!

One more thing, was your replacement element the same wattage as the old one? My experiance tells me that a 1K heater may be too small. I've always had better luck with at least a 1.5K heater vs. the 1K.

Hope that helps