CH overflow problem

I have an old conventional CentralHeating system. Recently it has developed a fault where water is expelled from the system back into the header tank and out through the overflow. As I am away from home for 3 months from this weekend I had arranged for a plumber to deal with the problem before I go. Unfortunately he has let me down and therefore I need advice on how to leave the system whilst I am away. I would normally leave the Central Heating on permanently at 11 degrees when I am away in the winter. With the fault, and the possibility of freezing weather, do I: 1. Leave heating on and leave the cold water mains on, or 2. Leave heating on and turn off the cold water mains?