bmw 325i se touring, I can hear the water boiling in the rad

Replace the radiator cap. Top off the coolant while you are at it and purge air out of the system.

If the coolant is mostly water, drain it and install 50/50 water and coolant.

Thanks and i have got a new cap as the O rings on it was worn, will put it on in the morning... I will do 50/50 antifreeze on the weekend...