Hot Water Cylinder Manufacturers in the UK

Hot water cylinders in the UK come from a mixed market: some makers build here, others import, and several sit inside bigger heating businesses. The cylinder trade is closely tied to the heat pump trade, because a heat pump needs somewhere to store the hot water it makes. At least 33 manufacturers supply air source heat pumps in the UK, with Mitsubishi Electric, Vaillant, Daikin and Samsung accounting for nearly two-thirds of total annual UK sales¹, and the main companies manufacturing air source heat pumps in the UK in 2024 were Mitsubishi Electric, Vaillant, Ideal and Octopus Energy, with a total market share of 34%¹. On the cylinder side, names such as Newark, Mixergy, Telford, Gledhill and Ideal Heating serve UK homes, and the makers publish very different levels of detail about what they cover².

For a household thinking about energy independence, the cylinder matters more than its modest price suggests. It is the store that lets a heat pump, solar water heating or off-peak electricity serve your taps, and newer models can hold their heat for up to 48 hours⁴. But a cylinder also creates dependencies: on the manufacturer's warranty terms, on an engineer who holds the right qualification, and on your water supply staying inside limits the maker sets. This page sets out who makes these products, how to size one, what the water quality rules are, and how warranty registration and servicing actually work.

UK manufacturers of hot water cylinders

The UK cylinder market is made up of specialist cylinder makers, heating brands that sell cylinders alongside boilers and heat pumps, and importers. Newark Cylinders, a UK maker, publishes guidance on unvented cylinders and their installation requirements². Mixergy makes smart cylinders in Oxford and publishes its full warranty terms online³. Telford and Gledhill are long-established names in the vented and unvented cylinder trade, and Ideal Heating sells cylinders as part of a wider heating range⁸. Beyond the specialists, the cylinder market overlaps heavily with the heat pump market, because most heat pump systems need a store.

The Heat Pump Association represents manufacturers which provide around 90% of the volume of heat pumps currently sold in the UK market⁹, and its membership includes the country's leading manufacturers of heat pumps, components and associated equipment, as well as energy companies, certification bodies, installers and training providers¹⁰. That breadth matters to a buyer: the cylinder, the heat pump and the controls are often sold as a system, and the warranty on each part can have different conditions attached.

For the wider picture of who stands behind each brand, see our full guide to home energy equipment manufacturers, and for the heating side of the market, heat pump manufacturers supplying UK homes and boiler manufacturers selling in the UK.

UK Cylinders and heat pump cylinders explained

The fastest-growing part of the cylinder market is the heat pump cylinder: a larger, well-insulated store designed to be heated slowly by a heat pump rather than quickly by a boiler. Where this segment sits in the UK manufacturing picture is quantified. In a baseline scenario, 33.5% of UK sales of hydronic heat pumps were UK manufactured, and one modelled pathway would increase UK hydronic heat pump manufacturing from 33.5% to 59%⁵. So a substantial share of the equipment heating the water in these cylinders is imported, and the same is true of some cylinder brands.

The maker side is concentrated. The main companies manufacturing air source heat pumps in the UK in 2024 were Mitsubishi Electric, Vaillant, Ideal and Octopus Energy, with a total market share of 34%¹. Cylinder makers position themselves around that equipment: unvented cylinders designed to take a low-grade, slow heat input, often with larger coils or plate heat exchangers, and pre-plumbed units that arrive with the pipework fitted.

For a household, the significance is practical. A heat pump cylinder is sized bigger than a boiler cylinder, it needs space, and its warranty may carry conditions specific to heat pump use, such as the plate heat exchanger softener rule covered below³. The dependence to note is that a heat pump cylinder ties you to the electricity system: it frees you from gas, but not from the grid, and not from the maker's terms.

Where Telford, Ideal Heating and smart cylinder brands belong

Telford and Gledhill sit in the traditional core of the UK cylinder trade, serving the replacement market for vented and unvented cylinders. The maker whose details are most fully documented in the public domain is Mixergy, which builds smart cylinders and publishes two sets of warranty terms, one for cylinders fitted before 3 June 2026 and one for those fitted on or after that date³. Its iHP X carries 25 years of cover on the stainless steel inner vessel, including the sensor strip, with registration and excluding labour⁷.

Ideal Heating is the clearest example of a heating brand that sells cylinders as part of a system. Its customer service and warranty team is based in the UK⁸, and is open 364 days a year¹¹. Its Logic Air heat pump range is designed for the UK climate and is partnered with Ideal Heating's pre-plumbed hot water cylinder¹². For a buyer, that pairing means one brand stands behind the heat pump, the cylinder and the commissioning paperwork, though the warranty terms for each product still need to be read separately.

Newark Cylinders, another UK maker, publishes the installation framework for unvented cylinders, including the Building Control notification requirement and the G3 qualification rule for installers². The connected end of the market, where Mixergy sits, adds a dependence the traditional makers do not have: the smart functions rely on the manufacturer's continuing operation and its online platform, and Mixergy's own warranty terms make annual monitoring via that platform one route to evidencing service³. A smart cylinder is only as independent as the company behind its app.

Choosing between vented and unvented cylinders for your home

An unvented hot water cylinder stores hot water and delivers it directly from the mains water supply, with no separate cold water storage tank². That is the core of the choice. A vented cylinder sits below a cold water tank, usually in the loft, and feeds the hot taps by gravity; an unvented cylinder takes mains pressure water and delivers it at mains pressure to every outlet.

The unvented route carries legal requirements. UK Building Regulations (Part G3) require that unvented cylinders are installed by a competent person who holds the G3 qualification, also known as the Unvented Hot Water Storage Systems certificate, and Building Control notification is required². A vented cylinder avoids those particular requirements but keeps the loft tank and its associated pipework.

A separate thermal store, whether hot-water only or integrated, is treated as if it were a cylinder for assessment purposes⁶, which matters when comparing what different products actually are. In practice, households moving from a combi boiler to stored hot water are making the switch in the other direction: one case study records a family replacing a direct combi supply with a new hot water system with a cylinder¹³. The trade-off is space gained in the airing cupboard's flexibility against space lost to the cylinder itself, and the gain in pressure and stored resilience against the loss of hot water if the boiler fails: with a combi, a breakdown removes hot water at once, while a full cylinder keeps its heat for hours, and newer models can hold it for up to 48 hours⁴.

How much space a cylinder needs: capacity, height and insulation

The size of hot water cylinder required depends on the amount of hot water your household typically uses¹⁴. The standard assessment tables give a normal hot-water cylinder size of 110 litres, with an indicative size of up to 130 litres⁶. Those figures are for a typical home; more bathrooms and more people push the requirement up.

Solar water heating changes the calculation: a larger hot water cylinder is likely needed, and this will take up extra room¹⁵. Heat pumps push in the same direction, because a slower heat input needs a bigger store to deliver the same burst of hot water. So the cylinder that suits a heat pump or solar home is usually larger than the one it replaces, and the space planning has to account for the height of the unit plus clearance for connections.

Lagging is part of sizing in a practical sense, because a bigger cylinder loses more heat if it is poorly insulated. In England and Wales, the cylinder should at least meet the minimum requirements of Approved Document L¹⁶. A hot water cylinder jacket costs about £30 in Great Britain and £30 in Northern Ireland¹⁷, while another estimate puts the cost at about £20¹⁸; the two figures differ, but both are in the same low band, and the jacket pays for itself in retained heat. The figures differ because they were read at different times, in November 2025 and December 2025 respectively¹⁷.

Chloride under 300 ppm, hardness and softener rules for water quality

Cylinder warranties are unusually sensitive to the water that runs through them, because stainless steel vessels corrode under the wrong chemistry. Mixergy's terms set the pattern. The water supply must not have a chloride content greater than 300 ppm³, and the updated terms state the same limit: water chemistry must remain within recommended limits, including chloride below 300 ppm⁷.

Hardness has two figures in the two versions of the terms, and they differ. The pre-June-2026 terms require that the water supply does not have water hardness greater than 270 ppm³. The terms updated on 2 June 2026 go further: in areas where hardness exceeds 200 ppm CaCO3, a water softener must be installed for the warranty to remain valid⁷. Where a plate heat exchanger is supplied with the cylinder for use with heat pumps, the property must be in a soft water area or the plumbing system must be deployed with a water softener³.

Two further points sit alongside the chemistry limits. UK building regulations advise that water cylinders, but not thermal stores, need to regularly reach temperatures of more than 60°C¹⁹, which is the legionella control measure. And if you have a hot water cylinder that stores water, the settings need to be set by a boiler engineer and kept hot enough to avoid the build-up of bacteria in your storage tank²⁰. A softener, in other words, is not the only condition: the temperature regime is part of safe operation too.

Registering within 60 days and keeping your warranty valid

Mixergy's warranty terms show exactly how a modern cylinder warranty is structured, and they are a useful template even if you buy another brand. Registration via the Warranty Registration Form must be completed within 60 days of commissioning, or of the first legal completion of the property⁷. The cylinder is warranted to be free from manufacturing defects for 25 years from installation, under the terms applying to cylinders fitted before 3 June 2026³, and the updated terms carry 25 years on the stainless steel inner vessel with registration, excluding labour⁷. Components carry 3 years from the date of installation³.

The conditions that keep cover alive are specific:

• Installation by a competent person in accordance with current UK Building Regulations and the maker's installation instructions⁷
• The Benchmark commissioning checklist completed and retained⁷
• An annual service carried out and documented, either in the installation manual or supported by proof of payment from the servicing installer⁷
• The servicing engineer registered with an appropriate competent person scheme, for example Gas Safe Register where applicable⁷
• Annual servicing, evidenced by a Benchmark service record or by subscription to the maker's care plan with annual monitoring via the online analytics platform³

The industry treats annual servicing as a warranty condition deliberately: making annual servicing a condition of the hot water cylinder warranty goes some way to addressing the problem of neglected stores²¹. Note the contrast with heat pump installation notification, where the deadline is 28 days²²: the cylinder's 60-day registration window is separate, and missing either can cost you.

Cover is also bounded by exclusions. The warranty covers corrosion, material defects and manufacturing faults⁷, but excludes consequential losses including property damage or loss of earnings⁷, and labour costs associated with replacement³. It is invalidated by frost damage, misuse, tampering, neglect, or modification other than by the maker³.

What to prepare when claiming on a warranty

A warranty claim moves quickly if the paperwork is ready before you pick up the phone. Mixergy's terms list what is needed: the product MX number, proof of installation and service history, and photos and a description of the issue⁷. The claim line is 01865 595 875, open weekdays from 09:00 to 17:00⁷.

What the maker provides is narrower than many owners expect. The warranty only covers replacement of the hot water cylinder, or the cylinder components as applicable³, and in the event of a valid claim Mixergy will provide a like-for-like replacement hot water cylinder³. Labour costs associated with the replacement are not covered³, so the householder pays the installer even when the part is free.

If the fault turns out to be a product recall rather than a one-off failure, the route is different: recalls are run through the manufacturer or its agent, as in one immersion heater recall where consumers were asked to contact the responsible company directly by telephone²³. Our page on home energy product recalls and safety notices covers that process.

G3 rules, Benchmark paperwork and the yearly service

The regulatory frame for unvented cylinders is Part G3 of the Building Regulations, which requires installation by a competent person holding the G3 qualification, the Unvented Hot Water Storage Systems certificate, and annual servicing by a qualified engineer². Benchmark is the nationally-recognised scheme that places responsibilities on both manufacturers and engineers to ensure best practice in the installation, commissioning and servicing of domestic heating and hot water products²⁴. Its purpose is to ensure that customers are provided with the correct domestic heating and hot water products for their needs, installed, commissioned and serviced in accordance with the manufacturer's instructions by competent persons, so that they are safe, perform with optimum efficiency and meet the requirements of the appropriate Building Regulations²⁵. An online integration of Benchmark with heat pump commissioning is set to make that process quicker and easier²⁶.

The industry body view is that servicing should be enforced, not just encouraged. The Heating and Hotwater Industry Council has called for heat pumps to have a mandatory annual service, and has recommended a review of Part G3 of the Building Regulations, which it believes is out of date and does not reflect the requirements of heat pump systems²⁷. It also sees the Benchmark service record as a means of maintaining high quality installation standards²⁷. Manufacturers recommend annual servicing of hybrid units, which require both gas and electrical skill²⁸.

The standards behind the equipment are set out in relevant British Standards, including BS EN 378-3:2008 on refrigerating systems and heat pumps, BS EN 15450:2007 on the design of heat pump heating systems, BS EN 805:2000 on water supply systems and components outside buildings, and BS5930:1999 with Amendment 2:2010 on site investigations²⁹. In practice, the annual visit is available through plumbing firms offering unvented cylinder installation and maintenance³⁰, and through service plans covering an unvented hot water cylinder and its installation pipework in a heat pump system, or a combined plan covering the air source heat pump, the unvented cylinder and the pipework for both³¹.

Why the Hot Water Association backs storing hot water

The Hot Water Association (HWA) is the industry body for the stored water side of the trade, and it works with the professional institutions to make the case for the cylinder. The Chartered Institute of Plumbing and Heating Engineering, in association with the HWA, hosted a webinar providing information and guidance on energy storage potential, grid enabled hot water stores and other thermal energy storage mediums³². That framing, the cylinder as a thermal battery, is the core of the argument: a store of hot water is a store of energy that can be filled when electricity is cheap or when the sun is shining.

The case rests on what stored water enables. An exhaust air heat pump can be used to heat water stored in a hot water cylinder for hot taps, showers and baths³³. Solar water heating needs the larger cylinder described above¹⁵. A household in one published case replaced a direct combi supply with a new hot water system with a cylinder¹³, and newer cylinders can hold their heat for up to 48 hours⁴. Set against that, the obligations are real: the legionella temperature requirement of more than 60°C for cylinders¹⁹, the annual service², and the water chemistry limits⁷.

For energy independence, the cylinder is one of the few pieces of household equipment that genuinely stores energy without a battery, and it is the component that makes a heat pump, solar thermal or off-peak tariff work as a system. The dependence that remains is on the maker's warranty terms, on a qualified engineer each year, and on the water supply staying inside the limits the manufacturer sets. Choose the maker with those conditions read, not just the litre figure.