What's the difference, if any, between maintenance manager and head of maintenance? Are they the same thing?
They might be, they might not. Depends on the company.
Some large companies might have lots of maintenance managers, each in charge of a team of maintenance engineers, and all the maintenance managers report to the "Head of maintenance".
So, I don't think you could make any assumptions either way.
A "Maintenance Manager" may have a "Head of Maintenance" above him or her but a "Head of Maintenance" cannot have a "Maintenance Manager" above them.
It does depend on the size of the company. If they have only one title they might have either, but if they have both titles then the Head will be higher up in the organisation.