<font face="Arial, Verdana">Sounds like your firmware uses relative extrusion by default while slicers use absolute extrusion coordinates. In Repetier-Firmware you have these commands</font>
<font face="Arial, Verdana">- M82 - Set E codes absolute (default)</font>
<font face="Arial, Verdana">- M83 - Set E codes relative while in Absolute Coordinates (G90) mode</font>
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<font face="Arial, Verdana">So here M82 in start code would solve it.</font>