Combi system pressure - why

[Johntheo5]

I wouldn't be too happy with a pre charge pressure of anything < 0.5bar, the pressure (air end) mightn't be high enough to push the bladder towards the water end, especially in the most common ones where the bladder is just shoved into the EV at the water end.

 

[potterton678]

It could be 0.3 or 0.5 bar if the if the highest point of the system is less than 3m (or 5m) above the boiler, and the boiler cutout pressure switch is set low enough. 1 bar is a convenient covering figure, which is OK for most installations.

The filling/top-up loop could be located at the same level as the highest radiator in the house.
Just saying.

 

[denso13]

The filling/top-up loop could be located at the same level as the highest radiator in the house.

It doesn't matter how high, or low, it goes, the pressure in the system is the same.

 

[fixitflav]

The filling/top-up loop could be located at the same level as the highest radiator in the house.
Just saying.

By system pressure I assume we mean pressure at the boiler. That's where the pressure switch is.
If the fill point is at a different level, that needs to be taken into account. It would be sensible to locate the pressure local to the fill point.
I suppose it's possible the fill point could be near an upstairs rad, but seems unlikely. A more likely reason for the fill point and PI being remote from the boiler is if the boiler is in the loft, to avoid climbing up there.