One fine winter day your I-CDTI will say - opps, today it's too cold. Especially if it has gone more than 120.000 miles. "Please change my glow plugs?". You might also see Error P1384 appear.
Because my car has reached 140.000 miles now, I've just made a preventive "summer change", I thought better now and not in the freezing rain. I've made a short tutorial (see attachement), my English surely is not the best, but perhaps it could be helpful for someone