Hi Roy,
All modern boilers have an over heat cut out to prevent damage to their heat exchangers. As you probely know long gone are the old cast irons jobs to be replaced with low water content tin jobs.
If you do not have correct circulation the boiler will quickly go to over heat and cut out so this could well be the problem.
As to a service, cast iron boilers should always be serviced every year as *Naughty Word* can drop onto the burner and 'chill' the flame this will produce CO.
Boilers such as your own do need less servicing despite what the manufacturer may tell you. I use a flue gas analyzer to test the products of combustion and have found that modern boilers can certainly go for two years sometimes three before they need a good clean.
One thing to beware off with a new boiler is the guarantee. Buried in your installation instructions is log to be signed by the service engineer. If you apply for a repair under the manufacturers warranty and the service log is not filled in they can walk away.
Colin H.
Never knew S L A G was a naughty word