[Bluewater335D]

On these cold morning, did you wait until the "glow plug light" - (a coil type symbol), goes out before you trying starting the car - ideally they need to preheat before starting the car - takes a few seconds

if you are thinking of fitting new glow plugs and controller, read up on this site before doing the work yourself

I have one plug recording an error - car normally starts first time, but yesterday I noticed that the glow plug light came on when I switched the ignition on

(Also the same with our 68 plate X1 diesel - again first thing in the morning glow plug light came on, which is normal in cold weather - start car when light goes out as with all diesel engines)

The worrying thing on your 320 is that if you have one glow plug down, (looks like No 4?), the car will probably not regen automatically - (this is reported on the Forum)