Basically, simplified, the programmer powers the valve motor only. When the valve moves over, it closes the microswitch inside the valve, and that microswitch completes the circuit with the boiler and pump.
If that switch isn't closing, then the pump and boiler will not run.
Obviously, the HW valve signal is "mixed" with the CH signal, so that either one of them can turn the boiler and pump on.
If that switch isn't closing, then the pump and boiler will not run.
Obviously, the HW valve signal is "mixed" with the CH signal, so that either one of them can turn the boiler and pump on.