I've meticulously taken care of my Rocket, but haven't used it for a year and went to turn it on and now as soon as I turn it on, the pump starts and never stops.

Any idea what's happening or how to fix it?

Well, a few dozen ideas until we narrow it down.
Is it trying to "boiler-fill" but not pumping? Trying to boiler fill but the valve is blocked or closed? If you touch the probe wire to boiler ground, does it stop?

What does the pump gauge show?
|Does the pump sound normal, quieter than normal or louder than normal?
If you raise the lever does the pump stop for a split second, then restart? Does water flow from the group with the lever raised?

Select the hot water function, open the valve, then turn the machine on. Does water come out of the spout?

Raise brew lever, turn on machine. Does water come from the group?

In either case, if the answer is no then if it was my machine, I would disconnect one heater element wire until I found the cause.