This temperature is set for 55'C ,first thing is to check if this temperature is correct if it is vastly different then the DHW control on the main pcb is at fault.However if it is marginally out or you feel that the 55'C is too hot for you then you need someone again with the understanding to adjust the DHW potentiometer on the pcb which is near the ST6 plug.I cannot say how much of a variation in temperature range this pot gives you but there maybe a man who can.
Guytawe
June 2010