300tdi water problems

Hi all, could someone tell me if i put a pressure tester onto the header tank and pressurise the water system, assuming no external leaks show and the pressure drops, would this confirm head gasket failure. Any help much appreciated many thanks
steve

most likey ,could be crack in block or head ,but gasket would be what id go for,remember most hgf are just stains not breaks

Thanks, when you say most likely is there anything else that could give same outcome of test?
Thanks
Steve

Could do a chemical test

Thanks for the help, but having read through some older posts i removed the 3 way pipe that runs from the thermostat housing to rad and header tank and one was blocked solid managed to clear out a load of brown gunge. Put all back together refilled and bled and now great, no cold water in header tank, heater hot and no problems. Not sure why this gave me a loss of pressure reading but happy all is now ok, thanks again
Steve