Hdi not starting occasionally

[aaron_one]

Hi guys, for the past few days the 306 has been iffy starting up, I wait for the plugs to warm and I've owned a couple of hdis but this hasn't ever happened before. It fails to start and then if I try again it starts, I'm worrying that one day it just won't start! It's had a recent service, the basic oil, oil filter, air filter and fuel filter but I did notice the gold ring wasn't there when changing the fuel filter, not sure if this matters at all? I never seen the glow plug light on but it briefly flashed when I started it up last.