On Fri, 22 Oct 2004 12:36:48 +0100, "Set Square"
wrote:


Unfortunately, your carefully logged details are missing one vital piece of
information - namely what the heating system was doing at the time in terms
of being switched on and off - either by a programmer or room stat.

Good point. Invariably the high pressure readings were while the
system was hot and the low readings were while the system was
elatively cooled-down.

Dave