I'm slightly confused..is it a sealed system or do you have a F&E tank in the attic which feeds the heating system?
If you have the tank in the attic then tie up the ball valve to stop the water filling the tank and filling the heating pipes..
If its a sealed system and the water spurts out the pipe when you put the mains on then yes its a water pipe and not a heating pipe
If you have the tank in the attic then tie up the ball valve to stop the water filling the tank and filling the heating pipes..
If its a sealed system and the water spurts out the pipe when you put the mains on then yes its a water pipe and not a heating pipe