How do I convert an EFI System Partition into a normal GPT partition?

Question

I had a Windows 8.1 that required a re-install. In the process, my 4TB secondary disk is now showing up in Disk Management as an EFI System Partition, with no volume.

In DISKPART, a volume is shown, with the info as "Hidden".

In MiniTool Partition Wizard the volume is shown as an EFI System Partition, but it's NOT listed as hidden. Using the tools in that software, I can successfully browse the data, etc. I've tried hiding, then unhiding the partition, without success.

So, my question is:

How can I convert this EFI System Partition back into an ordinary data partition that I can access and use?

(Unhide a EFI System partition doesn't help because my partition isn't flagged as hidden.)

Answer 1

Thanks to a friend, I discovered you can use gdisk from the GPT fdisk suite.

For the benefit of others, use gdisk 0: (substitute the number of the affected drive). Type p to print the list of partitions. The EFI System Partition will have a type of EF00. Enter t to change the type, select the number of the partition, and then type the code for the standard Windows partition, which is 0700. w will then write the changes, and after a reboot you should be back to normal.