On 10 Dec, 21:39, "Steve Walker" wrote:
Onetap wrote:
Like this,

http://img.photobucket.com/albums/v3...ff/Fortic1.jpg

Kin'ell, it's Stephenson's Rocket!

If I recall correctly I once met one of these things. It serves the
same function as the air bell innards of a primatic cylinder (spit)
and draining off the system will allow the air bell to re-establish.
Better to chuck it though and install a proper indirect system with a
seperate small heating header tank