it will taste burnt, if you open up your
coils it will also build up black gunk. depending how often you vape and at what temp/wattage for that coil it is easy to burn it out. but just because it has a burnt flavor doesn't mean the coil is burnt it could be lack of wicking.
often i find the coil i use to have issues with wicking so i just troubleshoot it how i can and it goes away then if it gets a very consistent burnt taste no matter what i do i simply toss it. this is why i moved to RDA's ASAP because disposable
coils are fricken expensive compared to building your own and i often find that they are tightly packed with cotten making it hard as hell to wick
juice.