Damage is Healed from Units at two specific times: 1. At the end of each player's turn. See rule 317.2. Ending Phase for more information. 2. During a Combat Cleanup. See rule 466.1. for more information about Combat Cleanups.
§ 143.3.b Core Rules PDF (officieel)
§ 143 Units have multiple Intrinsic Properties unique to them:
§ 143.3 Units can have damage marked on them.