Printer works but wont start a print.

Like the title says, everything works on my printer (motors, extruder, endstops, etc), however whenever I load the g-code in order to print something, my printer turns the heated bed and extruder to the correct temps, homes, then does nothing. It just sits there hovering around the required temps.

I am using the following:
Prusa Mendal
Slicer
Newest Sprinter Firmware
Ramps 1.4
Printrun

Can list some things that I should look at first?

When you say hovering, how close.
The firmware requires it to maintain a temperature within som tolerance for several seconds before it considers a temperature reached.
The defaults in some firmwares are very tight, I think Marlins defaults are 5 degrees and 12 seconds, but I'm not certain.

Its within the tolerances of what the stock firmware requires. Just to be sure, I went into the firmware and made them a little less restrictive but it didn't make a difference.

First thing to do is figure out what GCode line it's waiting on.
Usually it's the M109, you can delete it, set the temperature manually before tha print and see if that's the issue.