I'm sorry to hear you experienced problems with your cyan channel.Unfortunately, these printer models are prone to sudden clogging and flow problems like this.
How often have you been agitating the refillable cartridges, since installing them a few months ago? Refillable cartridges feed ink from the bottom, and we recommend agitating ink carts every week or two to keep pigment in suspension (all pigment ink settles, including Epson, but Epson carts draw ink from the middle)
Did the Epson tech replace the ink selector unit at the same time as the head?
Please let me know, thanks~ Dana