Welcome to the forum, George. You may have moisture in the contacts although they are sealed due to their location. If you trace the wires from the fan motor you should see a connector, disconnect and make sure it is clean and dry. Remove the multiplug from the sensor on the rear of the rad and using a piece of wire bridge the contacts in the plug (not sensor) the fan should start.
Also check the fuse for the fan, not sure where on a saffy.