yes it will.
pressure loss problems in general.
gradual loss---leak from system, whether its a radiator valve or relief pipe outside.
quick loss---expansion vessel fault---you set cold pressure to 1 bar, turn heating on, after 15 mins pressure is 3 bar plus and water escaping from outside relief pipe. heating goes off, system cools and contracts, and pressure drops to 0 due to loss outside.
observe what its doing. the guage will tell you whats up.
if you do get a quick loss of pressure but the guage does not rise to 3 bar then you may have a slightly bigger leak which could be just a badly seated p.r.v but like i say, do the test from cold if you want to rule out expansion vessel mentioned above
iain, December 2008
