On my stock Creality Ender-3 the PTFE bowen tube melts and starts to burn when it reaches 260 C that the printer allows out of the box, this commit decreases the HEADER_X_MAXTEMP in Marlin to decrease the max safe temperature to 240 to avoid this fire hazard.
This issue can be reproduced by using 260C hotend temperature on the printer without the filament and the PTFE bowen tube should start to smoke and burn in <50 sec
Appearently building Marlin on Arduino IDE version 1.8.x causes
the compilation error `using typedef-name 'fpos_t' after 'struct'`
Renaming `fpos_t` to `filepos_t` fixed the error.
Kreyren
Chris Steenerson
Felipe Siqueira Pinheiro
Naomi Wu