I think a important point may have been overlooked.
The expansion vessel needs to contain the Max amount of air when cold.
This is so the extra volume created when heated has somewhere to go.
If air has been lost from the vessel over a period of time, the vessel partially fills with water.
When the remaining air gets compressed the pressure goes much higher and opens the prv at 3bar.
There are two important points when correcting a expansion vessel.
The pressure needs to be around 1bar when cold. With heating on this will rise to around 2bar, but should never reach 3bar.
But the vessel needs to be empty, so any water in the vessel needs to be pushed back, so the system has to be open to atmosphere to discharge the excess.
If this is ignored, the pressure will go higher and the risk of opening the prv is increased
The expansion vessel needs to contain the Max amount of air when cold.
This is so the extra volume created when heated has somewhere to go.
If air has been lost from the vessel over a period of time, the vessel partially fills with water.
When the remaining air gets compressed the pressure goes much higher and opens the prv at 3bar.
There are two important points when correcting a expansion vessel.
The pressure needs to be around 1bar when cold. With heating on this will rise to around 2bar, but should never reach 3bar.
But the vessel needs to be empty, so any water in the vessel needs to be pushed back, so the system has to be open to atmosphere to discharge the excess.
If this is ignored, the pressure will go higher and the risk of opening the prv is increased
