The boiler provides a useful D.9 status to show if the HW mode is on or not. Ofcourse if you are standing in front of the boiler the flashing Tap icon is just as good. But if like me you are using a divisor to work out the current KW of the boiler based on the Partial Load and Modulation percentage, and if you are using two different Partial Load values for HW and CH, then you need to know, if you are in HW mode. Otherwise you get a weird looking calculated Kw reading from the boiler's returned values.