Expansion Vessel Repair London

Waterlogged expansion vessel

A waterlogged vessel is one that has filled with system water because the air charge has gone or the diaphragm has split. With nothing compressible left inside, every degree of heating pushes the pressure straight up until the safety valve lifts, then the system is short of water when it cools. You can often tell by lifting or tapping the vessel — a waterlogged vessel is noticeably heavy and sounds dead rather than hollow. Where the diaphragm is intact we drain and recharge; where it has failed the vessel is replaced, because a split diaphragm cannot be repaired.

• Expansion vessel full of water and heavy to lift
• Pressure rising to the safety valve when hot
• System needing constant topping up
• Recharge where sound, replacement where the diaphragm has gone

Expansion vessel diaphragm failure

The diaphragm is a rubber membrane that flexes tens of thousands of times over a vessel life, and it eventually splits — usually at the crease where it folds. The confirming test is simple: depress the Schrader valve core and see what comes out. Air means the diaphragm is sound and the vessel has simply lost charge. Water means the membrane has failed and system water is now sitting in the gas side. Some large commercial vessels have replaceable bladders and we will fit one where the shell is sound; sealed domestic vessels are always replaced.

• Water at the Schrader valve confirms failure
• Replaceable bladders fitted to suitable commercial vessels
• Sealed domestic vessels replaced like for like or upsized
• System flushed and re-pressurised after the repair

Expansion vessel leaking or losing pressure

Leaks happen in three places. The Schrader valve core weeps air and is a cheap replacement. The vessel shell corrodes, usually along the seam or where a damp plant room has attacked the paint, and cannot be safely repaired once perforated. The connection or flexible hose to the system leaks, which is a fitting or hose change rather than a vessel fault. We find the source rather than assuming, because replacing a sound vessel when the flexi was leaking is a common and expensive mistake.

• Expansion vessel valve leaking — core replaced
• Corroded or perforated shells replaced
• Leaking flexible connections and fittings renewed
• Expansion vessel with no pressure diagnosed properly

Failed expansion vessel and boiler pressure faults

A failed vessel does not just annoy you with the gauge; it damages other things. The pressure relief valve lifts repeatedly, picks up debris and then weeps permanently, so you end up paying for a safety valve as well. Constant refilling introduces fresh oxygenated water that accelerates corrosion and produces the black sludge that blocks heat exchangers. Fixing the expansion fault early is nearly always cheaper than the chain of repairs that follows it, which is why we check the vessel first on any pressure complaint.

• Repeated safety valve discharge resolved at source
• Pressure relief valves replaced where they now weep
• System water quality checked after constant refilling
• Filling loops and gauges renewed where faulty

Repair or replacement — how we decide

We repair where the fault is the valve core, a connection, a hose, a bracket or simply lost charge on a sound vessel. We replace where the diaphragm has failed, the shell is corroded or perforated, the vessel is badly undersized for the system, or the unit is so poorly located that it cannot be serviced in future. When replacement is the answer we fit the correct capacity, add serviceable isolation so the next check does not need the system drained, and mount the vessel on brackets rather than leaving it hanging on the pipework.