Same thing happened to me this morning on my PIXMA MG6821. I located & followed Cannon's support instructions to the letter; it failed to return the brick to service. So I did a lot of checking. Here's a summary:
As you may have seen, Cannon lost a class action suit about this print technology. Alas, it is far too late to join the class. The product group is clearly defective. If you're like me, you now have NO remedy for purchasing a defective product.
As you may have found on their website, Cannon has DISCONTINUED SUPPORT for the IFTTT platform, which includes this printer. I gather this applies to PAID support as well. DON'T WASTE YOUR MONEY. If you can't return it to the retailer, you're rogered.
As you may have found on these forums, if removing, servicing, and replacing the print head does not resolve the error, your only recourse is to buy a replacement print head. It can cost more than the printer did, and it is not certain to resolve the issue.
Given that this follows on an atrocious set-up/configuration effort when first purchased, after which I gave up the effort to set up for Air Print and used a printer cable, I am DONE.
My thinking is:
DO NOT WASTE TIME OR MONEY ON THIS JUNK. DO NOT BUY CANNON PRODUCTS OR SUPPLIES. YOUR ONLY OPTION IS TO SPREAD THE WORD so that others do not get RIPPED OFF.
