Any hot tub experts out there?

I bought a used hot tub, hooked it up, and here's what happened. First it gave me an error FL 1. I googled it to find out that it means the pump wasn't primed (obviously as I hadn't yet put water in). So I filled it and the the water was circulating nicely, but now the error code changed to ICE. I looked that up to and it means there is a risk of ice forming. I figured that error was to be expected as the water going in read 40 deg F, and the minimum set point is 65. I noticed a little red LED come on, which I presume means it was heating, and indeed it was as the temperature rose about 6 degrees over the next hour. Being that this was about 8:30 last night, I figured it wouldn't have nearly enough time to get up to 100 before I go to be, so I set it to 65 (the minimum and let it go all night.

Early this morning, I noticed the temperature had reached 65, and the water was noticeably warmer that the air outside. The pump wasn't running any more, but it did turn on when I pressed the button. So everything seemed to be working well.... here's where the trouble starts:

I decided to get it warming up to 80, so it wouldn't have to far to go when I got home from work, so I turned it up to 80 and went about my morning routine. I checked it an hour later before I left for work to see how it was progressing, but it temperature hadn't changed at all... It was still 65, and there was no LED indicating it was hearing up. So what could be wrong?