It's controlled by a dial the minimum setting for which is '1' (which the manual doesn't give a temperature value to ) and the maximum setting is a symbol that looks something like 'IIIII' which the manual says is 82 degrees. There are no inbetween values or symbols. There is no recommendation or suggestions in the manual re where the dial should be set for optimum / best for max efficiency. I found a link to an energy saving trust video but it was no help at all , any ideas?