Is the CPU fan RPM being reported in the BIOS?
Try downloading and installing HWinfo. Run it and check the box next to "Sensors only". Do not enable "Summary". Click ok. Scroll down to the H510MX/E v2.0 section where there should be a listing for the fan RPM for CPU, System 1, System 2, CPU_OPT, etc. and see if an RPM signal for the CPU fan is being detected and reported.
Considering you say "2700 rpm" I'm going to assume that yes, it is being reported, in which case I'd say you most likely have a problem with the PWM circuit on the CPU cooler. That means you most probably need to replace it with another cooler and I'd recommend not going with a stock cooler again since those are somewhat expensive on the aftermarket and you can get a really excellent cooler in the 20-30 dollar range in most countries. Especially since it's only an i3 that needs cooled.