Thanks for sharing the Cold Reset steps for the x476dw.
I have not seen a NVRAM Reset proceedure like that one yet, HP appears to want to make every new model be different. In previous touchscreen models you would only have to find the special spot on the screen to press and hold while booting. Now it sounds like they want you to tap a screen sequence too.
Does this mean that HP was not willing to service the printer under the warranty for this issue? Normally a boot problem can only be replaced by replacing the formatter and would be covered. Bringing the printer in for maintenance to perform this proceedure may end up costing you more than 50% of a new model and may not be worth it.