Unvented Cylinders

Unvented cylinders based in Stourbridge

Covering Birmingham, Dudley, Wolverhampton and the rest of the West Midlands

We are fully qualified unvented cylinder specialists based in Stourbridge, offering our range of services throughout the West Midlands including Birmingham, Dudley and Wolverhampton. 

An unvented hot water cylinder is a pressurised system which is fed directly from the cold mains water feed and therefore can deliver hot water at mains pressure, which is great for improving the performance of your shower and bath.

An unvented cylinder doesn’t require a cold water storage tank, which is ideal if you are pushed for space as well as offering more flexibility when siting the cylinder.

The water can either be heated directly via an immersion heater or indirectly via the central heating system, solar thermal technology or other renewal energy such as heat pumps and biomass. If you are considering using multiple fuel sources, you may wish to consider a thermal store.

The unvented hot water cylinder will require an expansion vessel to be fitted to allow the expansion of water in the system as it heats up. The unvented cylinder also comes with other safety mechanisms, such as pressure relief valves and twin thermostats.

To ensure safety and to comply with building regulations, it is essential that an unvented hot water cylinder is installed by a G3 qualified installer and serviced annually.

How do unvented cylinders work?

Unvented cylinders are limited by the 'power' of the mains water supply that feeds them, and in order to function properly require both adequate mains pressure and flow rate. Supply pressure should typically be in the region of 2 bar, preferable more, and capable of supplying the required flow rates. A Pressure Reducing Valve is required on all unvented cylinders to limit the pressure of the incoming mains water to a safe level at which the cylinder is approved to operate. The difference between pressure and flow is important to understand - a mains water pressure of 5 bar is no good if it is supplied through 100 metres of 15mm supply pipework. Mains supply pipe sizes and flow rates, as well as pressures, must be checked.

Call us today for free, friendly advice if you require a new unvented cylinder installed or repaired.

We have qualified G3 (this is the correct qualification for unvented cylinders which you require) engineers who can install or repair your cylinder. Your must ensure that unvented cylinders are fitted safely and to manufacturers specifications. UK Government created the Building Regulations G3 for this purpose.

We offer a free survey and quotation to discuss your requirements. We install multiple manufacturers of cylinders including Megaflo & Gledhill, Telford.

We recommend the following cylinder manufacturers: 

  • ATAG 
  • Vaillant
  • Telford

All cylinders installed by RJM come with at least 10 year guarantee

Unvented Hot Water Cylinders

An unvented hot water cylinder stores water that is directly supplied from the mains water supply into the property. The hot water is subsequently heated using electrical elements (immersion heaters) within the cylinder or indirectly from a boiler (this is explained further down 'Indirect vs. Direct'). Due to the cylinder operating at mains pressure, they are capable of supplying multiple outlets with hot water at excellent flow rates. With your hot and cold being mains pressure you will no longer require a cold water storage tank allowing more space in your loft. The term 'unvented' derives from the cylinder not being vented to the open atmosphere.

They are an excellent selection if you require instant hot water with great flow rates in multiple bathrooms and kitchens.

Unvented hot water cylinders are extremely dangerous to fit yourself. You must have a qualified professional install & maintain your unvented cylinder. These units are extremely dangerous when installed incorrectly.

Indirect vs. Direct

Essentially, the difference between an indirect cylinder and a direct cylinder is how the water is heated internally within the cylinder. You have two options:


The hot water is heated by an external power source, such as a gas boiler. These models usually have a backup immersion should the primary heating source fail.


The hot water is internally heated by immersion heaters within the cylinder.

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