Our old delivery truck seem to go though Bosch glow plugs a lot, but that engine was a terrible engine.
So if you're running Bosch glow plugs, you may want to try a different band.

 

We managed to have them replaced at a garage that sticks to it's 1 month warranty, closed Sundays so will visit tomorrow.
I'm thinkin the new plugs are not so good.

 

Good news.. went to the garage and they realised that they had set the relay settings the wrong way . Re-set them and this morning the truck fired up first time.
I really don't understand what they actually did, but all ok now !!!

 

Relay settings ???
Never heard of that one before, oh well, as long as it's working now.

 

Starts first time, although I was also advised to do what you suggested ie turn the key a few times on & off before starting.

I get all this info 3rd hand from my wife who understands very little about motors, as all the info was given in Thai.