might be best to start a new thread as im sure theres more people who would like to learn this information
Thanks John. I was overlooking thermal expansion coefficient on the left of boxes
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How would an expansion vessel under charged at ground floor level affect circulation in upstairs rads on start up @John.g?
I'll just answer this and maybe some one can/would transfer these posts to a appropriate thread.
If, for any reason, the pre pressure and fill pressure (due to leakage or improper charging or whatever) fall below the static head then the water level will start falling in the upstairs rads (first) and because the circulating pump is just that, a circulating pump, eventually there will be no circulation upstairs, after start up , and depending on the water temperature, the EV pressure will start to rise and may provide enough pressure (head) to allow circulation through these rads again. IMO poor or failed upstairs rad circulation is a indication of EV/water leakage problems.
Or to put it another way, if you pre charged to say 0.3 bar and initial filled to 0.3 bar then IMO there will be no upstairs circulation.