Water expands about 9% when it freezes. It's not a question of pressure relief, it's a question of the pipe bursting in multiple locations as it freezes end to

Water expands about 9% when it freezes. It's not a question of pressure relief, it's a question of the pipe bursting in multiple locations as it freezes end to end if you have lost heat in the house. The pipes don't leak until the ice melts.