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Unvented Systems


Many new properties and increasing numbers of extended premises are fitted with "unvented" hot water systems. These utilise the pressure from the cold water main supply to give good pressure to the hot water supply as well, without the need and noise of pumps.


With an unvented system, hot water flow, as well as cold water, is enabled throughout your property, without the need for pumps. Being linked to the incoming cold main supply, there is no requirement for stored water, eliminating the need for a cold water cistern.


To ensure proper and safe installation and on-going operation, the system and especially it's safety features, should be regularly serviced. THIS SERVICE MUST BE CARRIED OUT BY A PROPERLY TRAINED PERSON. You will know if they are trained correctly - ask to see their "Competent Person" identification, which will state "Unvented Hot Water Storage Systems" or similar, or will use the abbreviation "UHWSS".




Unvented systems, as the name suggests, work in a slightly different way to conventional, vented hot water systems.


Vented systems are open to the atmosphere, and water flow rate and pressure at the taps is dictated by gravity or by the use of a pump. The vented hot water cylinder is supplied via a cold water storage tank, often located in the loft (in a house) or on a shelf above the hot cylinder in the airing cupboard (in an apartment). Unvented systems rely on the cold water mains pressure for their flow rate and pressure. And there's a significant difference - the hot water is stored at pressure. Because of this, certain safety features are incorporated into the unvented system, to prevent excessive heat and/or pressure build-up and, in the event of a major system failure, to carry away what might become scalding-temperature hot water in a safe manner.


Manufacturers of unvented systems include Heatrae Sadia (Megaflow), Ariston (Primo, Classico), Santon (Premier PLUS), Range (Tribune), Telford (Tempest), Albion (Systemcyl), Vaillant (Unistore), and Worcester (Greenskies). Other manufacturers and models are also available - this is just a sample.


The manufacturers recommend a regular service of the system. Typically this should be carried out annually, and is usually a requirement to fulfil the terms of the warranty on the system. If there's a log book to record the servicing and other work carried out, make sure it's filled in by the Competent Person before they leave.


If you have any questions, or to arrange a service to your system, please contact us in the usual way - email or telephone:


Contact us at:       info@foscoe-plumbing.co.uk

    or by telephone:        01442 265 003

            and mobile:                07921 371 103