Did you prime the
coils?
Prime coil (one or the other):
1) drip a few drips of liquid directly into a new replaceable head.
2) do a few hard pulls to draw liquid into the head and let it sit for a moment before attempting to fire it.
The kanger subtank heads use organic cotton which burns very easily when dry. Once its burnt, just toss the coil because anything you vape out of it will taste nasty and/or harsh. Some people claim to have a sensitivity to cotton. Usually its not a flavor issue though, its more to do with tightness in the chest and such.