Our plumber replaced our immersion heater and thermostat a few weeks ago. He installed a Heatrae Pullin Gold Dot 27" immersion heater with thermostat. This, according to the literature, has a range of 10 - 60 deg C and is factory set at 60 deg C. The water in the tank does not get as hot as it used to with our old immersion heater. The little dial on the top of the thermostat is pointing to just a little past the half-way mark. Does this mean that it is Ok to turn it to a slightly higher setting?