The tub is wired directly into the main box, what your both saying sounds plausible...
as im typing just received this back from Balboa...
"Without knowing the specific Balboa system which is in the spa its hard to say for sure. The ML200 panel can be used on multiple systems and each system has its own aperage requirements and operation parameters. That being said, it does sound as though your system is working correctly and we do have many systems that are set to only heat with low speed to stay within the amp rating of the GFCI. Your system may have an option to operate more than just the low speed of pump one with the heater but I would need to know the exact Balboa system that is in your controller to know if that option is avaliable. Also, depending on the GFCI the installer of your spa put in, setting the higher amp setting may be to much for the GFCI to handle. If you have any further questions you can conact our tech support dept at 800-645-3201 Mon-Thurs 7am to 4 pm and from 7 am to 3 pm on Fridays. PST. Thank you. "
Think i will need to get back in touch with the showroom where i got it, but having contacted them twice regarding this with no reply, i am getting rather frustrated with their after sales service.
Thanks for your help in replying swiftly, will keep you updated.