Actually, it will go higher, but there is a thermocouple controlled cutoff. You can get it to go a bit higher by turning the motor on high about 5 minutes before you get in, but once you are in, agitating the water cools it down. There used to be a post on the web about using the adjustment for the thermocouple to "fool" the tub into heating up an extra degree or two, but I haven't been able to find it (and I'm not really sure I want to try).

Without the extra heat conserving stuff, it the tub would run for quite a while when trying to recover. What we got was a kit that had the insulating foam (for under the tub), a floating "heat blanket" (like a solar cover but stiffer AND a soft cover to go over the cover. Actually, in the US (again), if you don't have the soft cover, they won't warranty the vinyl hard cover!! The whole thing was about $300 (US), but it seems to have been a good investment.