I have added a couple of additional hosts to the cluster through the web0ui , but I can't update the current 'self hosting' host as the hosted-engine refuses to migrate.

HostedEngine:

• Cannot migrate VM. There is no host that satisfies current scheduling constraints. See below for details:
• The host 3 did not satisfy internal filter HA because it is not a Hosted Engine host..
• The host 2 did not satisfy internal filter HA because it is not a Hosted Engine host..
• The host 1 did not satisfy internal filter Migration because it currently hosts the VM..

I trawled google for awhile and found this post https://www.mail-archive.com/users@ovirt.org/msg34847.html

So I tried to enable 'HA Reservation', but I can't because host '1' can't be put into maintenance mode because HE can't migrate