Pumping air into combi expansion vessel - how many PSI?

[Dave£]

I checked the air pressure in my Britony 80 combi boiler's expansion vessel the other day; that's after I lowered the water pressure to about 0.8 bar. There was no air pressure at all - as I suspected.

I now need to know how many psi of air to pump into it when the water presure is, say, about 0.8 bar. I'm asking for a psi figure because my air pressure guage only has psi reading no bar reading.

The expension vessel was originally pre-charged to 0.7 bar according to the manual.

Thank you

Dave L

[Set Square]

1 bar = 14.5 psi - so, for 0.7 bar, you'll need just over 10 psi [10.15 to be exact - but I doubt whether your pressure gauge measures fractions of a psi]

[Dave£]

SS, Thank you for your help again. One thing I'm not clear about: At what pressure should the heating system water be when I pump the expansion vessel to 10psi? And, should the boiler be tuned on or off during this operation?

Dave L

[Set Square]

You must pump up the pressure vessel with the heating system cold and un-pressurised. At this point, the pressure vessel will be completely filled with air at 0.7 bar. *Then* use the filling loop to pressurise the system to around 1 bar, cold. *Some* water will enter the pressure vessel (on the wet side of the diaphragm), and will compress the air a bit more - but still leave plenty of expansion potential. When the system is hot, it shouldn't get to much more than 2 bar if everything is working correctly.

[Ed Sirett]

The FAQ may help (if it's read).