If reading is 0 or lower, you have an open circuit. This means 1 or both wires are not connected to maintain reasonably resistance. It could be from a broken wire or simply, an unplugged connection.

This usually means a wire to the heated bed or nozzle has been damaged or unplugged but not always. It could be that you have the target temperature set to high for the available power and it is taking too long in your current environment.

If an end stop (limit switch) is unplugged or isn't triggered during homing

Verify that all limit switches work (Serial Terminal using M119 command) and are contacted by the machine by hand.