Nozzles and tips how do you know when they are bad

[chuckinnc]

I just switched from AC stick welder to a mig welder using (75/25) argon/co2. How do you know when a tip or nozzle needs to be replaced?

 

[BrokenBiker]

because there is nothing left. Well, if you abuse them like I do. Usually when they start looking really grubby and wont clean up. The hole in the tips will wear.too so when its too big it womt give good contact and you might get some spattery welds