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.