--- title: "Expansion Vessel Replacement | Northstar Plumbing" description: "Replace a failed expansion vessel to restore stable pressure and protect your hot water system. Diagnosed, fitted and tested by qualified engineers." canonical: "https://www.northstarplumbing.co.uk/services/expansion-vessel-replacement" --- ![Technician in blue hard hat uses adjustable wrench on red and blue insulated pipes beside orange expansion tank](/_next/image?url=%2Fapi%2Fmedia%2Ffile%2Ftechnician-adjusting-pipes-wrench.jpg%3Fv%3D1768575117372&w=1536&q=75&dpl=dpl_DEc4fGhEc1SCRZZutzoEsRuDy1CJ) Hot Water Systems # Expansion Vessel Replacement [Contact Us](https://www.northstarplumbing.co.uk/redirect) An expansion vessel helps control pressure as water heats and expands in your hot water system. When it fails, you can get pressure spikes, dripping tundish or relief valve discharge, noisy pipework, and stress on the cylinder and valves. Expansion vessel replacement restores correct operation and helps protect the system from ongoing damage. ## What expansion vessel replacement covers A targeted visit to diagnose the fault, replace the vessel (or internal bladder type where applicable), and return the hot water system to safe, stable operating pressure. - Fault diagnosis to confirm the expansion vessel is the cause, not a pressure reducing valve or safety valve issue - Isolation and safe depressurisation of the hot water circuit - Correct sizing and selection of a suitable expansion vessel and fittings - Replacement of the vessel and any perished hoses, valves, or connection parts needed to complete the job - Recharge and pressure set-up to the manufacturer specification - Checks for leaks and correct operation during heat up - On unvented cylinders, verification of key safety components and discharge behaviour (work carried out by appropriately certified engineers) ### When this service is the right fit This is most relevant if you notice repeated discharge from the tundish, pressure relief valve dripping, rapid pressure changes on the gauge, or banging and water hammer as the system heats. It is also common after a cylinder service highlights a waterlogged vessel or a split diaphragm. Landlords and commercial sites often choose replacement to reduce call-outs and protect fittings from ongoing strain. ### What happens during the visit The system is assessed first, then isolated and depressurised so the vessel can be safely removed. The new vessel is installed, charged to the correct pressure, and the system is refilled and tested while heating to confirm pressures remain stable. If access is limited or the vessel is located remotely from the cylinder, the approach and any alternatives are discussed before work proceeds. ### Aftercare and ongoing value Once replaced and set correctly, you should see steadier pressure and little to no discharge during normal heat up. If your system is unvented, routine servicing helps keep safety devices, pressure settings, and discharge pipework working as intended. Any follow-up recommendations are kept practical, based on what is seen on site. [Contact Us](https://www.northstarplumbing.co.uk/redirect) ## Frequently Asked Questions How do I know if the expansion vessel has failed? Common signs include water discharging from the tundish or relief valve during heat up, a pressure gauge that climbs quickly, or frequent pressure-related faults. An engineer can test the vessel charge and check for a split diaphragm or waterlogging. Can an expansion vessel be recharged instead of replaced? Sometimes, yes, if the vessel is simply low on air charge and the diaphragm is intact. If the vessel is waterlogged or the bladder has failed, recharging will not hold and replacement is the reliable fix. Is expansion vessel replacement different on unvented hot water systems? Yes. Unvented cylinders have specific safety controls and legal requirements, and the work should be completed by an engineer with the correct unvented certification. The system is checked and set up to the manufacturer’s specifications after replacement. Will my water be turned off during the work? Usually, yes, the hot water system needs to be isolated and depressurised. In some setups the cold supply may also be temporarily shut off. You will be talked through what will be affected before work starts. How long does expansion vessel replacement take? Many replacements are completed in a single visit, but timing depends on access, vessel location, and whether additional valves or hoses need replacing. If there are wider pressure control issues, extra diagnostics may be required to resolve the root cause. 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