Best way to clean calcium build up out of a radiator??

Thanks every one.

I always use distiled water my self. But can not change what some one else did for 40 years to this pore thing.

I bought the CLR the other day, but read on the bottle not to use on coper or brass. So I was a little scared to use it.

And I thought about using the vinegar, but then I read that it dissolves lead.

And as I stated above there is no radiator shops around hear any more. The last one closed down a year ago.

Thanks!