From - Steam Generators, A Fault Guide for Drivers; CM&EE BR ScR Glasgow, 196?
A long time ago, British Railways were faced with a problem. It was halfway through the 20th century and the railway was still essentially Victorian in character. Modernisation was called for - steam engines had to go! Locomotives powered by steam were thermally inefficient but at least you could use the power of vapourised water to work the brakes, put water in the boiler or heat the coaches in winter, as well as just using it to move the train. With a diesel locomotive these auxiliary functions needed a little more ingenuity. The diesel engine provides mechanical energy which may be converted to electricity to power motors for moving the train as well as running pumps for cooling and lubrication; compressors or exhausters for braking; lighting and.. heating?
At the time of the 1957 modernisation plan, BR had huge numbers of locomotive hauled carriages on its books, all of which were heated exclusively by steam, if at all. While electric heating may be the obvious choice for use with diesels, the work required to convert the existing carriage fleet would be enormous. And so it came to be that diesel locomotives were being built in the 1950s and 60s with boilers for train heating. Technically they were referred to as "steam generators" and required diesel, electricity and water to be brought together in harmony to make high pressure steam. Perhaps unsurprisingly, these complex pieces of engineering gave a great deal of trouble at first and eventually BR bit the bullet and came round to a policy of electric train heating. The last steam heated ordinary service train ran in the mid 1980s, though sadly it is impossible to say precisely when and where.
Incidentally, the procedure above is for use with Stone Vapor train heating steam generators, models OK.4610, OK.4616 and OK.4625 only. I'm afraid I can't be held responsible for unintended consequences arising from you trying to blow the soot out of any other type of large industrial boiler using these instructions..