Dead black channel 1500W

Hi, Having real problems with the black channel on my 1500W.

Have done everything, cleaned wiper blade and capping station, scrubbed underside of head with bounty towel, forced PF through the channel. Nothing

Left the printer with piezoflush carts in it for months

All other channels are perfect

I got some lines in a nozzle check on that channel after a head clean. Then I performed another clean and it’s been blank since. Literally nothing printing from it.

What to do now? I had this machine from new.