was it self install or engineer?
are you connected to test socket?
go to hub manager then troubleshooting then helpdesk and post stats 1-12
Sorry but did you notice if openreach engineer or a contractor?
Have you tested your phoneline for any noise?
See this Helpfile http://support.zen.co.uk/kb/Knowledgebase/Performing-a-Quiet-Line-Test
If everything is quiet then :
Or it could be a faulty HH5 << a persistnt call to support in India should get you a new one sent out (once you have gone thru all their silly tech questions). This would at least eliminate the HH5 as the problem.
Other issues that spring to mind are line interference - this could be caused by an electrical device either within your own home that is switched on/off at the time you disconnect) - or could be in a neighbours home or on the street (like streetlights). These are obviously much harder to diagnose.
As per many other users who have had HH5 disconnection problems perhaps getting a seperate modem may give you more line stability. The recommended modem is the HG612 3B and is available from several online sites. The HH5 just connects to this as a slave device with the modem handeling the line connection.
is your openreach socket like this
if so then there should be a test socket behind the bottom half