--- title: "Unvented Cylinder Replacement | Northstar Plumbing" description: "Replace an unvented hot water cylinder with a safely installed, correctly sized unit. Includes checks, commissioning and compliance paperwork." canonical: "https://www.northstarplumbing.co.uk/services/unvented-cylinder-replacement" --- ![Wall-mounted boilers, white tanks and dense network of stainless-steel pipes with red and blue manifolds](/_next/image?url=%2Fapi%2Fmedia%2Ffile%2Fboiler-room-piping-manifold-filter.jpg%3Fv%3D1768575108210&w=1536&q=75&dpl=dpl_DEc4fGhEc1SCRZZutzoEsRuDy1CJ) Hot Water Systems # Unvented Cylinder Replacement [Contact Us](https://www.northstarplumbing.co.uk/redirect) Unvented cylinder replacement is the safe removal of an existing mains-pressure hot water cylinder and installation of a new unit that delivers reliable hot water, consistent pressure and compliant safety protection. It is ideal when a cylinder is leaking, repeatedly faulting, slow to reheat, or no longer meets your household or property demand. ## What unvented cylinder replacement covers A like-for-like replacement or upgrade, completed with the safety checks and commissioning an unvented system requires. - Site survey to confirm cylinder type, location, access and pipework condition - Sizing advice based on property demand, recovery rate and available space - Isolation, drain down and safe removal of the existing cylinder - Installation of the new unvented cylinder and any required valves and controls - Checks of key safety components (temperature and pressure relief, expansion control) - Review of discharge pipework route and termination for compliance - Filling, pressure testing, commissioning and performance checks - Handover guidance and relevant certification or notification where required ### When this service is the right fit You may need a replacement if your cylinder is corroded, leaking, losing pressure, tripping the immersion, or producing inconsistent hot water. It is also worth considering when parts are becoming uneconomical to repair, or when an extension, bathroom upgrade, or higher occupancy means your current cylinder is undersized. Landlords and small commercial sites often choose replacement to reduce downtime and improve reliability. ### How the replacement is delivered First, the system is assessed to confirm the correct cylinder specification and any constraints around access, electrics, and existing controls. The old unit is isolated and drained, then the new cylinder is fitted with the required valves and correctly connected to hot, cold and heating feeds. The system is then commissioned, safety devices are tested, and hot water performance is checked before sign-off. ### After installation: what you get and what to do next You will be shown how to operate the controls and what normal running looks like. If any pipework, valves, or discharge arrangements need future attention, this is highlighted clearly so you can plan ahead. For best reliability and safety, unvented cylinders should be serviced periodically to keep safety controls working as designed. [Contact Us](https://www.northstarplumbing.co.uk/redirect) ## Frequently Asked Questions Do unvented cylinders need a certified engineer for replacement? Yes. Unvented hot water systems have safety controls and legal requirements, so replacement should be completed by an engineer qualified to work on unvented systems. This helps ensure correct commissioning and the right compliance paperwork. How do I know what size unvented cylinder I need? Sizing depends on the number of bathrooms, typical simultaneous use, and how quickly the system can reheat. A survey will confirm the best capacity and recovery rate so you get consistent hot water without overspending on an oversized unit. Will you replace the valves and safety devices as well? Any unvented replacement must include correctly specified safety components, and worn or non-compliant valves should be replaced. During the job, the key safety devices are checked and the system is commissioned and tested. Can you replace an unvented cylinder if it is leaking? Usually, yes, but the priority is to make the system safe by isolating the water and electrics as needed. A leak may indicate corrosion or a failed component, and replacement is often the most reliable long-term fix. Will I be without hot water during the work? Yes, there will be a planned outage while the old cylinder is drained and the new one is installed and commissioned. The exact downtime depends on access, pipework condition and any remedial work needed, and you should be advised of this in advance. 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