In message , Keith J
Chesworth writes

I'll pass on the Organ, that is now totally refurbished and I doubt if
there is much by records of the original one left.

Because of the size and fame of the instrument there are in fact quite
detailed records of the original organ. The company that carried out the
recent restoration has a brief history on their website at:

http://www.mander-organs.com/html/body_news.html

Prior to refurbishment is was driven by an electric compressor.

According to the above site, the 1871 instrument was indeed steam
powered:

The wind-pressure was raised by steam engines in the blowing
room below the organ, driving six feeders. The high pressure was
provided by two blowing cylinders, 2 feet in diameter, each
containing a piston with a travel of 2 feet that provided the
vacuum on the upward stroke and the 30-inch wind pressure on the
return stroke. The plant worked well, and only one of the three
tenderers for rebuilding the instrument fifty years later
proposed to replace it.

The low-pressure engine is currently dismantled (but complete) and
housed at the Science Museum's storage depot in Wroughton near Swindon.

There is a picture of the high-pressure double-beam engine at:
http://www.allypallyorgan.org.uk/Pictures.html

Whether or not these were driven off a feed from the central boiler
house I don't know.

--
Paul Terry