In a word, yes - assuming that there are no isolator valves on the existing pipework. If you turn the main stopcock off, and allow the water to run, it will eventually stop as the loft header tank empties.
John
April 2009
Automatic Answer
We may have found other answers which could help you.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix plumbing.