Hello, i have a camray 5 oil boiler which supplies both my heating and hot water. I only need the heating on for a couple of hours per day but my question is regarding the hot water, is it best to leave the setting at 'on' for the water all day so the tank remains hot all the time or is it best just to have the water coming on for a couple of hours and reheating what quite often can be a full tank of cold water? hopefully this question is clear and any answers would be much appreciated, thanks!