Unvented Cylinder Wymondham: Expansion Vessel Repair

Following a routine gas boiler and unvented cylinder service in Wymondham, our team identified a failed expansion vessel on an unvented hot water cylinder. We sourced and fitted a replacement vessel with a custom bracket and adapted pipework, restoring the system ready for winter.

The problem

During a scheduled service of a gas boiler and unvented hot water cylinder at a property in Wymondham, we discovered the expansion vessel had failed. The expansion vessel is a critical safety component in unvented systems, absorbing the pressure increase as water heats and expands. When it fails, the system can become unsafe and the pressure relief valve may discharge water.

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Regular servicing of unvented hot water cylinders is a legal requirement under G3 Building Regulations and typically recommended annually. These checks ensure all safety devices — including the expansion vessel, temperature and pressure relief valves, and controls — are functioning correctly.

The repair

We sourced a replacement expansion vessel that matched the system’s specifications. However, the new unit did not come supplied with a suitable mounting bracket, so our team fabricated and installed a secure bracket to support the vessel properly.

Because the new vessel’s connection point differed slightly from the original, we also adapted the pipework to suit, ensuring all joints were pressure-tight and compliant. The system was then refilled, pressurised to the correct level, and tested to confirm everything was working safely.

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Why regular unvented cylinder servicing matters

Unvented hot water cylinders operate under mains pressure and store water at high temperatures, so their safety devices must be checked regularly by a qualified engineer. A failed expansion vessel can lead to excessive pressure build-up, causing the system to vent water through the pressure relief valve or, in worst cases, risking damage to the cylinder itself.

Our general plumbing services across Norfolk include G3-qualified unvented cylinder servicing, repairs and replacements. Catching faults early during annual servicing prevents costly emergency callouts and keeps your hot water supply safe and reliable through the winter months.

Frequently asked questions

How often should an unvented cylinder be serviced?

Unvented hot water cylinders should be serviced annually by a G3-qualified engineer to comply with Building Regulations and maintain manufacturer warranties. The service includes checks of the expansion vessel, pressure relief valves, temperature controls and all safety devices.

What does an expansion vessel do in an unvented cylinder?

The expansion vessel absorbs the increase in water volume as it heats up in a sealed unvented system. It contains a flexible diaphragm separating water from a cushion of air or nitrogen. When the vessel fails, the system loses its ability to safely accommodate expansion, causing pressure relief valves to discharge.

Can I service my own unvented cylinder?

No. Unvented hot water cylinder servicing and repairs must be carried out by an engineer holding G3 unvented hot water qualification. The work involves safety-critical components operating under pressure and at high temperature, and DIY work invalidates insurance and may breach Building Regulations.

What areas in Norfolk do you cover for plumbing and heating repairs?

EPH Services covers Wymondham, Norwich, King’s Lynn, Dereham, Thetford, Diss, Attleborough and surrounding towns and villages across Norfolk. We provide emergency callouts and planned servicing for boilers, unvented cylinders, central heating systems and general plumbing.

Need an unvented cylinder service or repair in Norfolk?

If your unvented hot water cylinder is due its annual service — or you’ve noticed pressure issues, discharge from the relief valve, or loss of hot water — our qualified team can help. We’re Gas Safe and G3-registered, covering Wymondham and all of Norfolk. Get in touch with EPH Services today to book your service or arrange a repair.