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Unvented Cylinder & Megaflo 

In Bushey

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Range Tribune

Range Tribune & ThermaQ make fantastic unvented hot water tanks for a lower cost than brans such as Megaflo. With external expansion vessels. for more information click  the image to find out more about what we can offer you.

Unvented Megaflo hot water tank

Megaflo are the only manufacture to design a unvented hot water cylinder that has a built in expansion vessel, making Megaflo the go to company for neat, clean & space saving. For more information click the image to find out more on what we can install for you.  

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If you need a 24hr Emergency Plumber for a leak or kitchen sink tap repair then call today and we can arrange for one of our Plumbers in Bushey to help you!

All our boiler repair and service engineers are gas safe registered. If you need a Local plumber near you we can help with over 35 years in the trade.

Unvented Systems Explained

There are two main types of water heaters used in residential homes today – vented and unvented. Even though vented systems are more common, unvented systems are still quite popular. They require less installation space and provide good flow rates to taps and appliances. Abbotts Maintenance experienced local plumbers have outlined the below guide explaining how unvented systems work.

Unvented hot water cylinders store water from the mains water supply. The water is heated either with heat from a boiler or using other electrical heating elements. This provides high pressure hot water supplies to feeding outlets. The increased pressure helps deliver better quality showers without the need for pumps. With unvented systems there is no need for a cold storage tank which helps free up space and requires much less pipe work.


Mains Water Supply

As unvented cylinders work from the power of the mains water supply, the mains pressure and flow rate must be adequate. Supply pressure should be around 2 bars and able to supply the required flow rates. A pressure-reducing valve is needed on all unvented systems to control the pressure of the incoming mains water supply to a safe level. Good plumbers will check the pipe sizes and flow rate of the mains supply in addition to the pressure.


Unvented systems have to provide a means to accommodate the expansion of the water in the cylinder as it heats up. Typically, two such methods are used – an external expansion vessel and internal air bubble. The former is basically a trapped volume of pressurised air and is held by a rubber diaphragm within a steel vessel. This is linked by pipe work to the unvented cylinder and as water expands, it's pushed into the expansion vessel, compressing the air within the diaphragm. Because the air is compressed, its pressure, together with that of the water in the cylinder, will increase. With the internal air bubble method, air is trapped in the top of the cylinder. The bubble compresses as the water expands similar to the way air is compressed in an expansion vessel. Annual servicing of the cylinder is needed to maintain the bubble. Local plumbers such as Abbotts Maintenance are experts in all plumbing work and can carry out annual services on all types of systems.

Safety Measure

Unvented Systems have two basic dangers that must be addressed. These are over-pressurisation and overheating. Over-pressurisation can be caused by a failed pressure reducing valve while overheating can occur if an unvented cylinder overheats and the water continues to increase in temperature and pressure until the cylinder can’t hold the pressure and splits. These dangers can be prevented by fitting an expansion relief valve and a temperature and pressure relief valve.


Qualified Gas Engineers & Plumbers

It is important to note that unvented systems require the skills of a qualified plumber. To work on an unvented water cylinder, plumbers must be qualified to work on unvented heaters and be registered. This is because unvented systems require a skill sets. At Abbotts Maintenance we have qualified plumbers to carry out such work.

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