I know I'm a little late to the party, but I can share some experience on when to replace a coil. Eventually, you'll stop getting the natural flavor of the liquid you're vaping and you'll get a taste that I can only describe as "unpleasant". In my case, it takes on a metallic, burnt taste. Once this happens, suffer through whatever is left in your tank and try to clean it.
There are many threads describing how to clean the Triton tank on these forums, so I won't waste time repeating it. Just use hot water if you don't have anything else handy, and let everything dry overnight. Next is where you roll the dice. If the coil and wicks are still good, you can reassemble the head, place it back in the tank and fill 'er up. If it tastes good again, you're in great shape. Sadly, sometimes it will be just as bad.
At that point, the wicks are probably burnt beyond repair, and you have two options: replace the wicks, or replace the entire head. Since I'm not a geek about wicks, and new heads are cheap, I'd just pop a new coil head in the tank and call it a day. At 5 for $12.50, it's really the best use of my time. Heck, if the coils were any cheaper, I wouldn't even bother cleaning them.
I'd echo Dave's statements on how long they last. It's a crap shoot. I did just literally have one last less than two weeks before going south. But that is the exception, not the rule.
Finally, as mentioned earlier, keep spares on hand. I've got 3 working tanks (two more on order), and about 10 coils sitting here, at any given time. That's just good sense. If it tastes nasty, you're going to be more tempted to go back to the analogs. So keep these cheap parts laying around so you never have to have a bad day in the vaping world.
Wes
