One tip I can give is about bleeding system after filling.
Obviously set heater controls to full hot … once system is filled get the engine started and then loosen the clamp on the highest pipe fitted to the duo valve …push the clamp off the pipe , loosen the pipe on the stub and push it nearly off the pipe and then use a thin flat blade screwdriver just gently lift the hose up to let air out of the system …. Leaving the hose on the stub of the pipe this way releases air in system but ensures the pipe is easy to refit .