I had a brand new Worcester boiler fitted in the summer and the installer left the water temperature at about mid-way on the dial. He said that it would need to be set higher in the winter. Is the setting in the photo - my latest effort - about right or should it be at maximum at this time of year? I'm a bit reluctant to go for maximum as I expect that the water will be near to boiling but I don't really know what to do.