E1 Thermal shutdown Marlin 2.0, Ramps

Here's the error log, any help gratefully accepted
Connected to Repetier host...
13:53:28.924 : X:0.00 Y:0.00 Z:0.00 E:0.00 Count X:0 Y:0 Z:0
13:53:28.924 : N12 M220 S100*82
13:53:28.924 : N13 M221 S100*82
13:53:28.924 : echoEBUG:INFO,ERRORS
13:53:28.924 : echo:No media
13:53:28.924 : echo:Unknown command: "M80" (power on)
13:53:28.924 : N14 M111 S6*82
13:53:28.924 : N15 T0*14
13:53:28.924 : N16 M155 S1*87
13:53:28.934 : echoEBUG:INFO,ERRORS
13:54:11.806 : Error:Heating failed, system stopped! Heater_ID: E0
13:54:13.886 : echo:Heating Failed
13:54:13.936 : Errorrinter halted. kill() called!
13:54:31.282 : N17 M999*28
13:54:31.292 : N1 M110*34
13:54:32.304 : N1 M110*34
13:54:32.304 : N1 M110*34
13:54:32.304 : N1 M110*34

After replacing thermistor, heater and RAMPS board, still got a "fail to heat" fault. when I converted from the original Melzi (Wanhao/Monoprice i3 duplicator) to RAMPS, I used USB as the SD socket was buried on the side of the display module. The problem seems to have arisen between prints, when I re-energize the temp settings (TPU, 225/45), which default to the lower PLA temps in the gcode. I did notice this new time that the temp readout on the repetier host screen showed something in the 180 area, which was a false indication, so perhaps something is wonky in the temp control algo. Watching on the Repetier screen during operation, the extruder temp stays withing +/- a few tenths of a degree, so control seems good in that way.
I cut a hole in the side of the control box, allowing me to access the SD socket, so I'll revert to SD operation again, maybe things will change.