Can air in a Hotwater tank, prevent the pressure release valve from working?
Air in the tank won't prevent the valve from opening. But if an electric water heater it can cause damage to the element. Just don't turn the water heater on until it is plumbed in then open a hot water tap and turn the supply to the water heater on. When the tank is full the tap will quit spitting air and run normally. After this is done it is safe to turn the heat on.