Just keep on turning it on and off and eventually it will fire up.
HM.
have you got air in the diesel pipe…you might have a little split in it where its drawing air in…just a thought
There is an inlet and outlet air pipe, makesure the inlet isn’t covered.
try cleaning or renewing the glow-plug
for the heater,check the filter fitted on the
fuel line from tank to heater if fitted may be
dirty ,
or try cleaning air outlet in the cab.if that gets blocked the heater overheats and shuts down.happened to me once and got shown by another driver .worked a treat after that
I had the same on a 55 plate FH. Replaced the pick up on the diesel tank, cleaned the guaze next to the night heater internal fan etc, still didn’t work.
I jacked the job when the boss told me to take an additional duvet cover if i was cold at night.
Try working more, You won’t get cold. 
Check you haven’t got so much junk crammed into the locker where the trunking is that it’s knocked the end of the trunking off the outlet or squashed the pipe. When investigating this, consider whether you can remember having ever used any of that crap. When you realise that you’d forgotten it was even there, warm up by dragging it all to the nearest skip.
just a quick one, you are best to run the n/heater at least a cpl of times in the summer months as the things fur up inside and come the winter cold nights the things dont work to good, just run them for 10 mins a few times in the summer,
sounds like your thermostat on the n/heater is going down the pan harry m,
Global warming!!!
or may be it’s just Failed Under ContinuousTesting.
Lucy:
Check you haven’t got so much junk crammed into the locker where the trunking is that it’s knocked the end of the trunking off the outlet or squashed the pipe.
Typical Stralis fault if I remember.
Ken.
Typical of any motor where the trunking is in a locker ie. most of them. Made a real dog’s dinner of a 4 Series Scania once… 