To answer my own question, if anyone else are having the same noobish problem as me
Quote a member from another forum:
Quote
printbus
You have EEPROM_SETTINGS enabled in your configuration.h, and according to the configurationStore.cpp file, the preheat parameters are some of the variables stored in EEPROM. I believe EEPROM settings take precedent over firmware settings, so what's likely happening is *old* settings in EEPROM are taking precedent over what you're trying to change in a firmware update.
One way to work around this would be to go to Control/Temperature on the LCD and then scroll down to PLA PREHEAT CONF. Set the preheat values how you want them, and then scroll back up and perform another store memory to update the EEPROM settings.