Several diesel glow plug problems can arise. Usually, glow plug failure is due to excessive heat, or high voltages reaching the plug. High voltage can be caused by a controller that is starting to go bad. Additionally, if there is faulty wiring, or a problem with the controller, the glow plug(s) may be receiving power all the time. Since the plugs are not designed to be on constantly, they will burn out prematurely. Moreover, excessive heat conditions can be caused by the engine’s timing, or fuel leaking from the injector(s). Of course, running gasoline in the engine will cause glow plug tip damage due to heat buildup in the pre-chamber.
For more info, see How to Replace the Diesel Glow Plugs