Combi pressure been at zero for weeks but still works

[ashtons99]

I'm puzzled by the heating in my daughters home. I posted a while ago about her Vokera boiler losing pressure daily when the heating was on. I was going round filling it every 3rd day or so but I've left it lately. It's been at zero for about 3 weeks but the heating has been operating fine.
The symptoms point to the expansion vessel, i.e. When the heating comes on and the system is charged to a bar or so the gauge goes up to over 3 bar

After giving up on trying to get a plumber round after the 4th one didn't show I thought I would see how it went if I didn't top it up. We are going have another attempt at getting a plumber interested but it just seems very strange that the boiler hasn't shut down

 

[transam]

can depend on what the boiler has fitted

some did not have a low water pressure cut off switch , but only have a water/pump proving switch so providing it detects flow (some Biasi's) . water movement it will continue to work. even when the gauge is on 0 or very low

some boilers have both devices lwp switch & a flow switch (CSI 120/150)

incidentally I am not aware as to what method is used on your vokera ????????

 

[DP]

I would suggest you get the boiler looked at like yesterday.

There are Vokera models where pump proving switch sticks in pump proved position, boiler will then dry fire and melt everything in the combustion chamber.

Your daughters boiler, you filling it, your call