Thanks for the suggestions! I cleaned out the filter which had a lot more small plant material on it than I realized. I also cracked open the manual (thanks to CanadianSpaTech) and realized that some jets weren't working due to the diverter knobs being broken so ordered a couple new ones and, like magic, they all work again!
Also programed the filter for a 20 hour cycle (as opposed to the standard 24 hour) so I can can be in the tub 8pm-midnight without the circulation pump on. A small victory but it makes me happy.
All this has led to the water staying between 103-102 which I can live with. This summer when the tub is drained I will, if I'm feeling adventurous, test the heater element. Installing a new one looks straight forward enough. Is it surprising that a heater has lasted 15 years?
Anyway, thanks for the ideas & hope spring has appeared where you live!