Controller that takes as an input the boiler water temperature
TBoi and the system on command onSys, and
outputs the on command for the pumps onPum and the
boiler onBoi.
The pump on command is the same as the system on command. The
boiler is switched on if the boiler temperature TBoi
falls below 70°C and if onSys=true, and it
switches off if either TBoi exceeds 90°C or if
onSys=false.