The Aura boon says:
Choose a single bane or boon which uses the same attribute that you used to invoke Aura. The maximum power level for the chosen bane or boon is one-half the power level of your aura.
The duration for aura is 'Sustain Persists', meaning that it only continues you use a minor action each turn to keep it active.
However, heal has a duration of 'instantaneous', so regularly healing only applies once. Would it apply multiple times if was used with aura?
It gets even more confusing when the regeneration boon is introduced, as that has a duration of 'sustain persists' and has an effect like heal, so it would be pretty useless as an aura if an aura of healing worked multiple times.