TH16 AUTO and SCENE conflicting

Hi Dear Friends ,
I have the following demand: i have connected TH16 to a pump which heats a drinking hotwater tank (DHW) with serpentine from a heat buffer connected to my heating boiler !
When i set only Auto mode it works ok , but when the temperature of the buffer is less than the one set in the dhw tank it still switches on and doing nothing (it can not reach the requested temperature)
I have another TH16 connected to the buffer which controls the heating boiler !
How can i block the DHW Th16 from engaging if buffer temp is lower (this i can do with a scene) but then it is not switching on when the buffer temp is already good !