When I used silica I cleaned heads by soaking them with the top post off in a shot glass filled a little under half way with isopropyl rubbing alcohol for about an hour, very cheap, found in most pharmacy sections of supermarkets. Then rinse them in distilled water overnight and set them out to dry in the morning. Water by itself can dissolve many remnants off your coils/wick, but depending on the juice you use it wont. Isopropyl rubbing alcohol contains a mix of water and alcohol, both of which are great solvents, so what the water doesn't get, typically the alcohol will.
If I found that the coils were still gunked up, I mixed isopropyl (70%) with water, 50/50, and dripped it on the exposed head one drop at a time, pulsing the battery as I went. I am not really sure why this worked to clear out extra gunk, I suspect it is because the extra heat supplied during the process helps increases the solvency of most chemicals, allowing them to dissolve and then vaporize. The reason for the pulsing is because once the liquid evaporates the coil will typically glow, and the legs of the coil will get very hot often burning the rubber grommet in the base of the atomizer, which results in a permanent disgusting taste.
If this still doesn't work, disassemble and build a new one.
With your particular battery type you don't need to worry about messing up rebuilds. Even if you short out, or build a coil with too low of a resistance, the battery will auto shutdown. This is probably why some of your builds have worked and others haven't.