Worcester Greenstar 28i - CH and HW fine - 0 bar pressure?

[Chick21]

I repressurised the system before Christmas and saw only today the pressure had dropped down to 0 bar, however both hot water and CH seem fine.
I checked the towel radiator and it seems to be the culprit as only the bottom half was hot, so bled this one and repressurised the system.

Could this be a leak somewhere (can't see any evidence) or other causes?

 

[lame plumber]

pressure gauges are notoriously unreliable so 0 could be 1/2 a bar. check all rad valves for leaks or rusting first if pressure keeps falling best to call in a gsr techie to help

 

[plumber0808]

Definitely should not be dropping that quickly, maybe get someone in to have a good look

 

[justlead1]

You can get a pressure gauge with a 1/2" male thread. Isolate a rad (tun off both ends) unscrew plug or air valve either end at top of rad, screw in gauge, turn valves on and read off pressure. It should be the same as boiler gauge. (assuming you have not got the system running whilst carrying out this check)
I would also check the pressure release valve discharge pipe. Water lost from here often means that the expansion vessel need topping up with air.