Copper heat blocks and heater calibration failures with 6.4.0-RC
It seems running heater calibration is hit or miss when using a copper heat block. I accidentally reran it (I needed to run other tests) and it kept failing. This creates an annoyance because the printer will display nag screens that the calibration is not complete when turning on the printer and I have to hit "OK" to continue. It will also do the same before starting a print. To make it pass I swapped out for an aluminum heat block.
I haven't dug into the firmware source code yet, but if I were to guess, the PID settings in firmware are calibrated to an aluminum block and the heater test is probably testing for ramp up time which then fails. Otherwise, the copper blocks work fine.
RE: Copper heat blocks and heater calibration failures with 6.4.0-RC
I'm using a copper heat block on my Core one and don't experience this. Since you've changed the heat block the heater set screw must be snug, one possibility. Try a different heater? This is a test of that element after all. If there's some on hand, maybe some thermal paste.
RE:
The test doesn't pass consistently. Otherwise there is nothing wrong with the heat block. It comes up to temp set in g-code and stays there.
I replaced the heat block with aluminum (same heater and thermistor) and it passed 100% of the time. I'm not doing anything crazy with the grub screw like making it too tight. My guess is that there is probably a timer and if the test temp isn't reached before the timeout, it fails.