Why won't the print start when M109 command is used?

When I try to start a print job that contains the M109 (wait for temperature to be reached) command, it just hangs.  Here is my gcode:

M190 S55 ; set bed temperature
M104 S200 ; set temperature
G28 ; home all axes
G1 Z5 F5000 ; lift nozzle

M109 S200 ; wait for temperature to be reached

If I manually preheat the bed and extruder and comment out the M109 line of code the print starts with no issue. 

Something that may be related, during the preheat step the bed temperature display in Repetier-Host shows 54.90 even though the LCD display on the printer shows the value going up and down.  After the print starts, the display starts working again.


  • Do you have TEMP_HYSTERESIS set different then 0? Then you would need to hold temperature stable for a while before finishing. Normally it is ok to be at target temp. -1°C to stop waiting in firmware. But 54.90 is bed temperature and M109 is wating for extruder temp. to reach 200°C.
  • Yes, that was the problem. My extruder takes a while to stabilize at the desired temp.  I bumped up the TEMP_HYSTERESIS value to 6 and now it's printing fine.  Thanks.
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