An unvented cylinder gives you mains pressure hot water at every tap, with no cold tank in the loft. For many homes in Chorley it is a genuine upgrade over an old gravity system, but it is not right for every property. Here is what actually matters before you book an installer.
A traditional vented system relies on a cold water storage tank in the loft feeding a copper cylinder, and the pressure at your shower depends on how far below that tank it sits. An unvented cylinder does away with the loft tank entirely. It is fed directly from the cold mains, so hot water arrives at the same strong pressure as your kitchen cold tap, upstairs and down.
The practical benefits are a powerful shower without a pump, freed up loft space, less pipework to freeze in winter, and no risk of tank contamination. They suit larger households in particular, because a 210 or 250 litre cylinder can comfortably run two showers at once, which a combi boiler usually cannot.
The single biggest factor is your incoming mains supply. An unvented cylinder is only as good as the water feeding it, and we would want to see roughly 1.5 bar of dynamic pressure and a flow rate of around 20 litres per minute or better. Much of Chorley on the United Utilities network has decent mains performance, but older properties with original lead or half inch supply pipes can fall short, and some outlying spots around Heapey, Brindle and Wheelton vary. A proper installer will measure pressure and flow at your stop tap before quoting, not guess.
You also need somewhere to put it. Cylinders typically range from about 120 to 300 litres, and a common 210 litre model stands around 1.5 metres tall. An airing cupboard, garage or under stairs space often works. Finally, the safety discharge pipe (the D2 pipe) has to run to a safe, visible external point, which occasionally rules out awkward mid terrace layouts without some creative pipework.
This is the part homeowners are most often not told. Because an unvented cylinder stores hot water under pressure, installation is controlled under Building Regulations Part G3. The installer must hold a current G3 qualification, and the work must be notified to building control, which for Chorley means Chorley Council unless the installer self certifies through a competent person scheme such as Gas Safe or APHC.
A compliant installation includes specific safety devices: a temperature and pressure relief valve, an expansion vessel or air gap, a tundish, and correctly sized discharge pipework. If any of that is missing or the paperwork never arrives, you may have trouble with insurance claims or selling the house later. Always ask to see the G3 card and confirm who is notifying the work.
As a realistic guide, a straight swap of an existing unvented cylinder in the Chorley area tends to fall somewhere between £1,200 and £2,000 supplied and fitted. Converting from a vented gravity system, which involves removing the loft tank, rerouting pipework and running the discharge pipe, is a bigger job and more often lands in the £1,800 to £3,200 range depending on cylinder size and how far pipe runs have to go. Brand matters too: cylinders from the likes of Megaflo, Gledhill, Telford or OSO carry warranties of up to 25 years on the stainless steel vessel.
Most straight swaps are done in a day. A full conversion usually takes one to two days, and you should expect the water off for several hours on the first day. Ask for the benchmark commissioning checklist to be completed and left with you, and book the annual service, because the warranty on most cylinders depends on it.
Published 17 August 2026 by Red Leaf Plumbing & Heating.
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