def set_dhw_on(self, until=None):
        """Set DHW to on, either indefinitely, or until a specified time.

        When On, the DHW controller will work to keep its target temperature
        at/above its target temperature.  After the specified time, it will
        revert to its scheduled behaviour.
        """

        time_until = None if until is None else until.strftime(
            '%Y-%m-%dT%H:%M:%SZ')

        self._set_dhw(status="Hold", mode="DHWOn", next_time=time_until)
Set DHW to on, either indefinitely, or until a specified time.

        When On, the DHW controller will work to keep its target temperature
        at/above its target temperature.  After the specified time, it will
        revert to its scheduled behaviour.