Have now done all that and here in all their glory are the pictures via photobucket assuming ive done it right
http://s220.photobucket.com/albums/dd34/daniellemartine12/
Thanks for comments- the reason I ask about draining the cylinder is the stat looks unlike the ones on eg screwfix website - it has two wires coming out the end, seems to be moveable in and out and of a hole in the cylinder witha nut on the end - I think it is a combimation cylinder - we have no...
Is it advisable for a DIYer to change a cylinder stat - is there anything particular I need to know? Do I have to drain the system? Any help much appreciated