As the title says, I'm trying to figure out the signal from my boiler's controller that indicates hot water demand. Unlike ancient systems that operate the timer and thermostats at mains voltage, this one has 7 pins of an 8 pin connector connecting the controller to the boiler's main board.
I thought at first I could piggy back the connections to the integrated diverter valve but have established that this is in fact a stepper motor controller by what seems like a L293D chip (the upshot being that the wiring to the diverter is doing fancy things to precisely control the rotation of the motor and is not giving me the simple binary signal I am looking for).
Having also drawn a blank searching for all variations on "DW-20 pinout" I can think of, I've learned that Bosch commonly use a proprietary bus called EMS and that others interface to this through a 3 pole jack plug. Trouble is, there is no such plug or socket in my system, so if the internet is to be believed the EMS bus might utilise some of the pins on the simple header style connector. Or it could just set various pins high or low to indicate central heating demand or hot water demand.
Problem is that any detection skills I may have had in my teens are long gone and I'm embarrassingly incompetent with my multimeter (I can figure out if something is live at mains voltage, what my car battery is doing or if there is a break in a wire but not a great deal else. I only get Arduino circuits working by following instructions to the letter).
Please can someone help me point me in the right direction to deduce which pin (if any) on the controller indicates HW demand? Ideally, I'd like to do this without frying the boiler main board.
Many thanks in advance.