Potable Expansion Vessel
Potable Expansion Vessels accommodate expanding water, and pressure fluctuations. If the vessel becomes filled with water it can no longer perform its function.
Although these Potable expansion vessels are technically NOT a part of the heating system, typically they are supplied with the Heat Pump along with an Inlet Group manifold. These parts may be covered under some Heat Pump Manufacturer warranties.
Waterlogged potable expansion vessels are a common issue in newer homes with Booster Pumps. Repressurising or replacing the vessel ensures your heating system runs efficiently and safely.
Where is my potable expansion vessel?
They are usually beside or above your water cylinder or indoor Heat Pump unit. The potable expansion vessel is usually white, grey, or blue. The label on the side of the potable vessel will say “POTABLE” or have an icon of a Tap or shower
You may also see a red vessel which is typically the heating vessel. The heating vessel rarely becomes waterlogged in low-temperature heat pump systems.
Both vessels require regular maintenance to operate effectively.
Waterlogged potable expansion vessel pulling its poorly secured bracket off the wall. This vessel increased in weight from 2Kg when correctly pressurised to 20kg when waterlogged. If this had completely detached from the wall it would cause damage to pipework and leaking.
How can I tell if my expansion vessel is waterlogged?
Gently tap the vessel. A properly functioning vessel will produce a hollow ringing sound while a waterlogged vessel will produce a dull thud.
Why is my heating system banging or groaning when I turn on water?
Commonly, as a potable expansion vessel begins losing its pressurised air charge it can start making strange noises that sound like loud banging or groaning.
Often a vessel with no pressurised air charge at all or a fully waterlogged potable vessel will not make any such sound. However, repressurising an expansion vessel that has been waterlogged can sometimes cause it to vibrate or groan when boosted water is used. Repressurising might only restore its functionality temporarily and the vessel may have to be replaced. If your vessel has been waterlogged for a while, your pressure relief valve may be dripping and may also have to be replaced.
There are a few other reasons these sounds can happen:
An incorrectly sized expansion vessel,
The pressure reducing valve set too low, or
A booster pump defect
