Keep working that head. Here's a tip. Underneath the machine is a hole.. below the capping station. It uses a slotted tool to manually screw the capping station motor up and down. (My buddy threw ours out, so I cut a slot on the end of a piece of 3/8" nylon rod. )
With POWER OFF screw the capping station down.
Slide the carriage to the left a bit to see the caps.
Clamp the drain lines ABOVE the pump with hemostats. Keep them clear of the carriage.
Fill each cap with flush.
Slide the carriage back and align it to the caps.. (there are guides on the left and right that stick down for that).
Raise the cap station assembly so the caps compress onto the heads to form a seal.
Let it soak. For a weekend. This will put solvent directly in contact with the yuck that's blocking the k/c head.
Remove the hemostats.
Run a cleaning cycle (press clean and power at same time)
Likely will resolve. If not, repeat the process. It takes time for the chemicals to work.
I'm pretty sure the 540 has similar tech to the soljet2 we've got. We use this cleaning method monthly just cause.
its only a freaking
sign!