Rio 2500

When I bought my tank, I got a Rio 2500. After about 5-6 weeks it began
to lock up when the power was turned on. I could get it to work by
taking it apart and putting it back together before turning it on, but
it was unreliable. One blackout could wipe out my tank.

So, to fix this, I bought another Rio 2500 and a new impeller for the
first, and this worked well for about six weeks. Then the same thing.
Now I am running the first with the new impeller.

What is up with these things? Do they need a new impeller every month
or so?

Are these things just pieces of junk?

Is there some way to repair or modify them?