i am using  brushless esc 20a rating with emax cf2812 and did successfully test the four pairs once but now one of my esc is being heated up and motor doesnt do anything after initialization beeps are produced. according to specifiactions of my esc , it already has heat sinks attached. all other 3 pairs are working fine. what should i do??

What is brand of ESC?
Try to run only this motor-ESC separately. You can switch the esc and motor with working esc and motor to identify if the problem is in motor or ESC.

 motor is running fine.sir i have already done what you suggested. the problem is in esc. esc is NR-BLDC-MD20 from nex-robotics. please help

Did you smell any smoke when first time this problem occur? It looks like ESC is burned and you will have to replace ESC.

Which prop are you using with motor? Did you check how much current is being drawn using watt-meter.

i am using 8x4.5 prop from rcdhamaka. i was suggested to use 7x6 but these were the only ones available. moreover 8x4.5 produce much larger thrust, so i used them. maximum current that can be drawn by these motors is 10 ampere

Neha, just remove the motor and receiver (if have ) from ESC.. just plug in to a battery source.. observe for any heating up.. if it is ok, just connect an other motor.. if it is ok, check the BEC line.. and if the ESC still heating without motor and BEC load, please remove the heat srink sheeth from ESC with a blade, very carefully, without damaging any components, and check any MOSFETs for burns.. and check the leackage current on PCB.. check protector once.. check the BEC low drop devices for any shortage.. if find, just replace the devices..

Your ESC got Damaged. Just use any other ESC preferably higher amps one.
If you want to repair, just replace large capacitors first.

Thanks.

my esc has burned and will have to buy another. thank you all.