I was recently trying to heat my hot end to 250° C to try and get PETG to stop stringing. When I did this, I realized after about 10 minutes of waiting that it never quite got there. It would only get to ~247-248° C, fluctuating in that arena.
This started me to wondering, is there a rule of thumb for heater replacement? Should you replace it in a given amount of time, when it isn't doing the job anymore (like mine seems to be doing), or just replace it when it dies?
I see no benefit to changing a heater that's performing acceptably. The only rationale I can think of for a predictive or preventive change-out would be to head off the cumulative effects of repeated wire flexing. That would be devilishly difficult to predict.
Unless one was about to kick off an extremely high value print due to high consequence schedule constraints or high material cost, it's difficult seeing a pre-emptive heater change being justified. Even then, it becomes a risk comparison between wear-out of the old and infant mortality of the new.
I don't think there is any rule for when to change the hotend since it's dependent on a lot of factors like the filament types you print with, if your nozzle hits the bed often, etc.
Generally, I check the nozzle every two weeks or so. I end up replacing it about every 6 months, from a moderate amount of printing.
