If you guys are getting stuck with this (ie can't start car, can't get to work etc) buy some Easy Start or similar. One short squirt into or around the air intake will be enough to get any sound engine going. Forget all the old wives tales about engines getting addicted to it and it doing damage etc, I've been using it for years (and years and years
). It's only a volatile fuel, just don't use too much. Obviously a proper fix is a better solution but hey getting to work is the priority here.
Really in these sort of temps a few seconds cranking to start a diesel is not too critical a fault, some engines are better than others. Of our 2 cars the Mondeo starts instantly but the 1.9 Vectra (same engine as Alfa) always needs the heater plugs or will crank over just like your Alfas.
I might also add that checking glow plugs out of the engine is not the correct way to check them. Getting hot individually is not the same as being inside a freezing cold engine. There is a rig that measures resistance and temp in an operating condition and I've only ever known one specialist that has one. When faced with this problem I change the glow plugs for new ones as do most garages.
The glow plug error light can be triggered just by one faulty plug not necessarily the whole lot or the whole system. Usually in this condition it will go off after a few minutes.
@Heraldcapri.... what oil are you using? Spinning very fast? Your hydraulic tappets could be sticking, losing the compression when the oil is too thick in cold weather.
All of this just thoughts and general knowledge, don't take it as gospel truth for every car