A build up of rust can eventually cause radiators leaking water, as sludge can collect within the appliance to cause rotting from the inside out, and small holes to form on the radiator surface. This type of leak is regularly referred to as a pinhole leak.
There are a number of measures you can implement to stop a radiator leaking water if rust does have a negative effect, some representing a more permanent solution than others. Our blog, How To Fix A Leaky Radiator, explains how you can combat the problem in greater detail.