If you haven't already it’s also worth considering fitting a new fuel filter as if only slightly blocked this can lower fuel supply pressure and choke the main pump, the pump will be more sensitive to this when its cold as diesel thickens considerably with low temperatures.It may have developed an air leak on the fuel supply pipe from the tank to the engine. The engine has no separate lift pump and relies on the built in one in the injection pump. If a leak has developed on the fuel suction pipe then air entering the system will air lock the pump. Try pumping up the fuel using the hand pump in the engine bay on the filter housing, then crack off / loosen each injector pipe in turn while cranking the engine and getting an assistant to operate the primer. This will expel air from the injection side and the engine should fire up. The problem will be cured by checking the supply pipe along its length for signs of leakage and repairing any you find.If you daub each pipe joint with heavy grease and the issue goes away then wipe the grease away one at a time to highlight the problem joint
its possible that if the vaporiser was on all the time then yes this would give excessive fuel consumption, however its not a common fault
if you pull fuse F9 in the engine bay fusebox then this should disable it?
also check for binding brakes, check that all the wheels can be turned freely by hand, and free off any sticking calipers
Incorrect wheel alignment:
Check all the tyres for signs of uneven wear if it has any then get it checked out at a place that does 4 wheel alignment not just front tracking and ensure tyres are pumped up to their recommended maximum
Injectors are clean and not dribbling - add a bottle of injector cleaner to the tank
Use good quality fuel - from my own findings its worth paying the extra for BP or shell as typically you'll get another 10% fuel saving which outweighs the cost over supermarket fuel.