Fresh Install of F20 failed to install bootloader

[Arthur Dent]

I have finally found the time to upgrade my desktop machine from (ahem)
F16 to F20.

It is my habit to have 2xOS partitions, 1 partition for /home and 1 for
swap. Each time I upgrade I actually do a clean install in the
last-but-one OS partition (i.e. in this case where the F15 had
previously been) leaving the current (i.e. in this case F16) untouched.
This way I can simply mount the previous install and copy across any
configs etc.

I used a (tested) F20 64bit full install DVD (not the live disk).

I could make neither head nor tail of the new anaconda partitioning
system (and I still don't know if I will have successfully pointed the
F20 install to the existing /home partition - I know it seemed to insist
on creating it's own /swap even though there is a partition dedicated to
that and formatted as such for the existing F16 install).

Anyway the first attempt failed completely - locking at the screen where
you have to create a root password and user.

The second attempt seemed to go through OK, installing all the packages
etc. but I had to take a phone call at the point where it said it was
doing "post-installation configuration". By the time I came back, the
screen was informing me that Fedora 20 had been successfully installed -
reboot to start using it.

The reboot put me back into my old F16 install (at least I know that
hasn't been screwed up!) with the grub menu offering me only varying
kernels from F16.

It seems F20 has not installed the bootloader properly.

What are the steps for getting F20 to boot (while, if possible still
giving me the option to boot into F16)?

Thanks

Mark