What are some signs to look for in knowing when to replace pump?

Well stop working seems not to be getting any power to pumptrol, well,etc

By pumptrol do you mean a Square D Pumptrol pressure switch?

Start looking for reasons power not getting to pressure switch, such as tripped breakers.

Start at the power source, (the breaker box) and track the voltage back to the control box.
If the contacts are closed check the outgoing voltage to the pump.
Use a voltmeter that can handle 220 volts and use extream caution.
Let me know the rusults. Good luck, Tom