Printer stops heating, thinking he does

Hi i have a problem and can't figure out what it is.

I installed the repetier firmware and everything works.

Accept when i start printing, the temperature of the bed and extruder starts to drop. when it is to low for the print the software states: HEATING EXTRUDER but it does not.

The temperatures keep falling and so the extruder motor stops to.

it keeps thinking that it is trying to heat the extruder and plate but it is not.

If i install the sprinter firmware this problem does not present itself. i added the config files of both firmwares.

All help is welcome! i'm realy stuck

Greets Niels