I also have GBT mobo and if I remember correctly, there are 3 options you can select for CPU fan. One is AUTO, second is PWN and I don't remember the third one (it should be the one for the max RPM)... Did you tried all 3 of them?
You should take a note that fan on cm 212+ @2000rpm is very loud! Why do you need them to run at max when colder days are already here?
If nothing else works, connect both fans to PSU and they should be running at max RPM...