def set_dhw_on(self, until=None):
        """Sets the DHW on until a given time, or permanently."""
        if until is None:
            data = {"Mode": "PermanentOverride",
                    "State": "On",
                    "UntilTime": None}
        else:
            data = {"Mode": "TemporaryOverride",
                    "State": "On",
                    "UntilTime": until.strftime('%Y-%m-%dT%H:%M:%SZ')}

        self._set_dhw(data)
Sets the DHW on until a given time, or permanently.