A large number of expansion vessels are replaced unnecessarily. Generally, this is because the engineer has found water discharging through the Schrader valve and has drawn the conclusion the diaphragm in the expansion vessel is defective. The diaphragm in expansion vessels is constructed from thick rubber and rarely fails. Usually, the water found discharging through the Schrader valve is a result of condensation that naturally accurses within the air side of the diaphragm. You can expect the condensation to be as much as 0.5 litres.

Step 1: Discharge the system pressure, using a drain point and not the pressure relief valve.

Step 2: Push in the Schrader valve and remove the air from the vessel.

Step 3: If water is discharged from the valve, remove the Schrader core and connect a gauge tube to the expansion vessel.  Note, water inside the vessel may be condensation and not the expansion vessel diaphragm split or leaking.

Step4: Increase the system pressure, slowly, to 1.5 bar. This will push any water/condensation from the air side in the expansion vessel out via your connected gauge hose.

Step5: If the expansion vessel diaphragm is split, the water will continue to discharge via you connected gauge hose. If this is the case, a replacement expansion vessel is required.

Step6: If the water stopped, this is a good sign the diaphragm is intact. Release the pressure from the system through the drain-off.

Step 7: Renew the Schrader valve and connect your pump.

Step 8: Re-Charge the expansion vessel to the manufactures stated pressure or 0.7 bar cold. Note, the system drain-off must be open.

Step 9: Leave your pump attached for 5 minutes. If the diaphragm is split, the pressure will drop, if it stays stable, then the expansion vessel is serviceable.

Step 10: Close the drain-off and re-pressurise the system to the manufactures stated pressure or 1.2 bar cold.

Step 11: Check the Schrader valve with leak detection fluid.

Useful Tips For How To Recharge An Expansion Vessel:

1: If changing the expansion vessel required taking the boiler off the wall, consider fitting an external expansion vessel.

2: When pumping up the expansion vessel, if the gauge rises very quickly after 1 or 2 pumps then it’s likely there is a blockage or restriction in the pipe or hose connecting to the expansion vessel.

3: IF the Schrader valve is difficult to access, consider using a flexible valve extension.