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I am having issues with the new Rev B HE280 hotend (no thermal fuse) with my Rostock Max V3. The issue is once there is a request for temperature of the hotend, either from the calibration program or a manual input on via MatterControl, the temperature setpoint is not acknowledged. The Rambo board does not acknowledge the heater set point and continues to call for heat. If the unit is turned off and then back on, the hotend heater comes on without any input action. If I plug in my old hotend, the heater does not come on automatically (there is an issue with the existing heater and that is why I am replacing it with a Rev B assembly).
I have contacted the SeeMeCNC support staff, and we have yet to be able to resolve the issue. I have uploaded new firmware to my Rambo board, and we have also tried another Rev B HE280 hotend assembly. We get the same results. Any input in regards to experience with the Rev B HE280 hotend and a Rostock Max V3 would be greatly appreciated.

You state that the old hotend heater doesn not come on automatically,,,, Does it come on when the RamBo calls for heat?

When Mosfets fail, they normally fail "On", causing the heater to be on all the time.

What I mean by "coming on" is the heater LED is ON, on the hot end. The heater on the old hotend has failed. The only reason I don't think it is a Mosfet that has failed in the "ON" position is because I am able to "turn off the heater" (turn hotend heater LED ON & OFF) with the old hotend. The other thing that I have not been able to fully diagnose is if I allow the printer to sit over night, come back the next day, and start up the unit, the heater on the Rev B hotend does not automatically come on. It is only after I call for heat on the Rev B hotend, either by manually toggling the hotend heater ON in MatterControl, or run the PID hotend calibration program.