What Is an Unvented Hot Water Cylinder?
An unvented hot water cylinder — the best known brand being Megaflo — stores a large volume of hot water and delivers it at mains pressure directly to your taps and showers. Unlike older gravity-fed systems that rely on a cold water tank in the loft to create pressure, an unvented system takes water directly from the mains. The result is powerful, consistent hot water throughout your home.
This makes a significant difference to shower performance in particular. Many London properties — especially period conversions across Battersea, Chelsea and Kensington — have poor shower pressure because their hot water is gravity-fed. An unvented cylinder transforms this.
How Does It Work?
The cylinder is fed directly from the mains cold water supply and heated by your boiler or, in some cases, an immersion heater. Because it's sealed (unvented), it operates under mains pressure. Safety devices — including a pressure relief valve and an expansion vessel — are fitted to manage any thermal expansion safely.
Because these systems operate at mains pressure and involve high-temperature stored water, installation must be carried out by a G3-qualified engineer. All Unique Plumber engineers hold the required qualification.
Is an Unvented Cylinder Right for Your Property?
An unvented cylinder works best in properties where:
- You have good incoming mains pressure (we'll check this before recommending)
- You have multiple bathrooms and want strong hot water pressure throughout
- You want to remove the cold water tank from your loft
- You're renovating and want a modern, high-performance hot water system
- Your current gravity-fed hot water pressure is frustratingly weak
It's less suitable if your incoming mains pressure is poor, or if you have very limited space for the cylinder (a typical unit is around 1.7m tall and 500mm diameter for a 150-litre model).
Popular Brands We Install
We install Megaflo (Heatrae Sadia), Gledhill, Telford, OSO and Vaillant unvented cylinders. We'll recommend the right size for your household based on the number of bathrooms and typical hot water usage.
Unvented Cylinder Service and Maintenance
Unvented cylinders should be serviced annually by a G3-qualified engineer. The service includes checking the pressure relief valve, expansion vessel pressure, thermostat function and all safety devices. Neglecting this can void the manufacturer warranty and — in rare cases — create safety hazards.
Areas We Cover
We install and service unvented hot water cylinders across SW London including Battersea, Chelsea, Clapham, Wandsworth and Fulham, and across NW London including Golders Green, Finchley, Harrow, Wembley, Ealing and Kensington. See our hot water systems service page for full details.