I have a 1997-98 model year Cal Spa Genesis w/4 HP 2-speed pump.

When I power up the hot tub it goes into it's automatic 4-hour filter cycle and will heat up. After it reaches temperature, and after filter cycle is over, it will shut off normally. However, it will not automatically restart to maintain heat or filter like it used to

Any suggestions?

Does it have different modes, like economy, sleep, standard, etc?

Be sure it's in the correct mode.

No, not that I'm aware of. When it is first powered up, turning the breaker on, it is supposed to go into filter cycle for 4 hours. Now it just hums until I press the jets button. It will then turn on in high jets mode. I can then cycle the button through light mode, then back to low jet mode and it will run for it's 4 hour cycle. When the temp drops below set point it will not start up again unless I press the button. It will then just click and finally start up after a couple of minutes.

I replaced the motor recently, but this problem existed before.

Sounds like your control is either in economy or sleep mode if it has them...

how many buttons and what kind of display does this thing have?

Post a photo of it if possible.

Did you say it just hums unless you push the jets button?

Then high speed comes on, then you can get low speed to run?

I hate to say it, but that pumps broken again.

I'm betting the "humming" sound you hear is the sound a motor makes when it gets power but won't turn.

And why after it reaches temp, but won't turn on again to maintain proper temp.

The topside control is not digital. It has a temp control knob and one pushbutton. Push it once for low jets, a second time for high jets and a third time for the light to come on.

I don't believe it is the pump motor. It will run on low and high, and it will run it's 4-hour filter cycle. It heats up just fine and seems to work properly (i.e, I can cycle it through low/high/light modes) while it is running. I just don't understand why it won't start on it's own. This morning I shut the breaker off, then turned it back on after about 20 seconds. I then opened the cover, pressed the control button once (it just clicked), then closed the cover. After about 2 minutes, the motor started on it's own in low speed and began it's 4-hour cycle.

It's a mystery....

You can tell very quickly with a voltage meter.