Hot Water Cylinder Manufacturers in the UK

A hot water cylinder is the one piece of household plant that stores energy as heat rather than buying it at the moment of use, and the UK market for them is substantial: around 500,000 hot water cylinders are installed, new and replaced, every year¹. The makers fall into three groups. Dedicated cylinder manufacturers such as UK Cylinders, Telford, McDonald Water Storage and Newark Cylinders build vented, unvented and heat pump cylinders, often to order. Boiler and heat pump manufacturers such as Vaillant and Ideal Heating supply matched or pre-plumbed cylinders alongside their appliances. And a smaller group, led by Mixergy, sells connected cylinders that heat only part of the volume and report back through an app.

UK Cylinders is described as the UK's largest manufacturer of heat pump cylinders and a leading supplier of unvented hot water solutions, working from three Yorkshire facilities under ISO 9001 quality standards². Telford states it manufactures in the UK and offers the widest range of copper and stainless steel cylinders available, sold through plumbing and builders merchants³. McDonald Water Storage states it is the only company in the UK that manufactures all its vented cylinders to BS1566 standards, and the only cylinder company specialising in exact like for like replacements for copper thermal stores⁴.

For a household, the independence argument is straightforward and limited. A cylinder decouples the moment heat is generated from the moment hot water is drawn, so it can be charged by a heat pump, a solar thermal panel, an immersion heater running on cheap or self-generated electricity, or a boiler. It does not generate anything. It remains dependent on whatever heat source fills it, on the mains cold supply for an unvented model, and, for smart models, on a manufacturer's cloud service and a company that has to stay in business for the life of a warranty that can run to 25 years.

Who makes hot water cylinders in the UK

The domestic cylinder market is unusual in that a large share of it is still made in Britain. Telford states its cylinders are manufactured in the UK using premium quality materials, that its stainless steel and copper storage range supplies the plumbing and heating industry nationally through local merchants, and that next day delivery is available on some lines³. UK Cylinders manufactures unvented cylinders for both traditional and renewable systems, supplying social housing providers among others, with nationwide coverage². McDonald Water Storage supplies vented and unvented cylinders across the UK and Ireland, and offers replacements described as covering any make, any model, any shape, any size, any capacity⁹.

Materials divide the market. Cylinders are manufactured from copper or stainless steel, with mild steel solutions that in a domestic application are glass lined, predominantly used outside the UK¹¹. Bespoke makers extend that choice to the grade, meaning thickness, of the copper or stainless steel used¹².

Heat pump cylinder supply overlaps with the heat pump industry itself. There are at least 33 manufacturers supplying air source heat pumps in the UK, with Mitsubishi Electric, Vaillant, Daikin and Samsung accounting for nearly two-thirds of total annual UK sales; 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%¹³. Industry modelling puts the UK-manufactured share of hydronic heat pump sales at 33.5% in a baseline scenario, against a scenario raising it to 59%¹⁴. The Heat Pump Association represents manufacturers accounting for around 90% of the volume of heat pumps currently sold in the UK market, and its membership includes manufacturers of heat pumps, components and associated equipment as well as energy companies, certification bodies, installers and training providers¹⁵.

Further brand detail sits on the heat pump manufacturers and boiler manufacturers pages, and ownership questions on who owns which energy brand.

UK Cylinders and the heat pump cylinder segment

Heat pump cylinders are a distinct product rather than a conventional cylinder relabelled. A heat pump delivers water at a lower flow temperature than a boiler, so the internal coil has to be larger to transfer the same heat, and the cylinder is normally a mains pressure unvented design¹⁷. That is the segment UK Cylinders is described as leading, and its output covers both traditional and renewable systems from the same Yorkshire plants².

Integrated heat pump cylinders, where the heat pump and the store are supplied as one unit, are quickly increasing in popularity in the UK¹⁸. Exhaust air heat pumps, which draw heat from air leaving the building, can also heat water stored in a cylinder for hot taps, showers and baths¹⁹. Ideal Heating pairs its Logic Air range with what it describes as its best in class pre-plumbed hot water cylinder, and states that its customer service and warranty team is based in the UK and open 364 days a year, with the range designed for the UK climate²⁰.

In practice the household consequence of a heat pump cylinder is a larger box and a longer reheat. The store has to reach temperatures that satisfy the legionella guidance: UK building regulations advise that water cylinders, but not thermal stores, need to regularly reach temperatures of more than 60°C⁸. That last step is usually done by an immersion heater, which means a period of direct electric heating in every cycle. Grid flexibility can be earned from a cylinder but only in one direction: a Mixergy cylinder, and hot water cylinders in general, can only provide certain services to the National Grid operators, because the electrical energy is converted to hot water and cannot be converted back to electricity¹.

Telford, Ideal Heating and the connected cylinder makers: where each fits

Maker claims of this kind are promotional and should be read as such. What distinguishes the groups practically is how the cylinder is bought: Telford sells through merchants for an installer to specify, Ideal Heating supplies a cylinder matched to its own heat pump, bespoke makers build to a measured space, and Mixergy sells a controlled appliance with a subscription option attached. Brand-level detail on Mixergy cylinders, Heatrae Sadia and Megaflo, Vaillant and Ideal Heating is held separately.

Unvented or vented: which cylinder suits which home

An unvented cylinder stores hot water and delivers it directly from the mains water supply, with no separate cold water storage tank in the loft²⁴. It delivers mains pressure hot water throughout the property and is described as suited to modern homes, renovations, or properties wanting mains pressure hot water throughout²⁵. The trade-off is regulatory and financial: an unvented installation requires Building Control notification, and vented cylinders tend to be cheaper than unvented because they are relatively simple in construction and operate at lower pressure²⁴.

• Unvented: mains pressure at every outlet, no cold water storage tank, no loft space needed for a feed cistern, but Part G3 installation and notification apply²⁴
• Vented: gravity fed from a cistern, simpler construction, lower operating pressure, generally cheaper²⁶
• Thermal store: in SAP treatment, a separate thermal store, hot-water only or integrated, is treated as if it were a cylinder²⁸

For independence, the distinction matters in a power cut and a mains failure. A vented system will still deliver stored hot water under gravity from its cistern; an unvented one depends on mains pressure being present. Both depend on the heat source, not on the cylinder, for the energy in the tank. Newer cylinders can hold heat for up to 48 hours, which sets the practical limit of how long a household coasts on a charge²⁹.

Sizing: capacity, height and lagging add up to the space you need

The size of cylinder needed depends on the water demand, the number of occupants and the frequency of baths and showers³⁰, and more broadly on the amount of hot water a household typically uses³¹. For larger properties, a direct hot water cylinder of 300 litres or more is indicated³⁰. RdSAP's reference table gives a normal hot-water cylinder size of 110 litres, with an indicative size up to 130 litres²⁸. Bespoke manufacture spans a far wider band, from 8 litres to 2,000 litres in various heights, diameters and orientations, vertical and horizontal⁶.

Physical fit is decided by more than litres. A published domestic sizing guide records a 40 litre cylinder at a shell diameter of 280 mm; its two listings of the height for that capacity, 720 and 645, disagree, and the discrepancy is unresolved³². Bespoke options include variable coil quantities, sizes and positions as well as upgradeable insulation thicknesses, and insulation thickness adds to the external dimension even where the stored volume does not change¹².

Two things push a cylinder larger than a household expects. Solar water heating needs a larger cylinder, which will take up extra room³³. Heat pump systems need the larger coil described above. Where the cylinder replaces a combi, the space has to be found from scratch: one recorded case saw a household replace direct combi boiler supply with a new hot water system with a cylinder³⁴.

Insulation standards apply to the finished installation as well as the product. In England and Wales, the cylinder should at least meet the minimum requirements of Approved Document L³⁵. For an older uninsulated cylinder, a jacket costs about £30 in Great Britain and £30 in Northern Ireland³⁶, with a separate estimate of about £20³⁷; both are consumer guidance figures rather than quoted prices.

Water quality limits: chloride below 300 ppm, hardness and the softener condition

Stainless steel cylinders are sensitive to water chemistry, and manufacturers write that sensitivity into the warranty rather than the specification. Mixergy's terms dated 2 June 2026 require water chemistry to remain within recommended limits, including chloride below 300 ppm, and state that in areas where hardness exceeds 200 ppm CaCO3 a water softener must be installed for the warranty to remain valid⁷. The earlier terms, for cylinders fitted before 3 June 2026, required that the water supply does not have a chloride content greater than 300 ppm and that water hardness is not greater than 270 ppm³⁸. The two documents therefore set different hardness thresholds, 200 ppm and 270 ppm, and which applies depends on the installation date.

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 deployed with a water softener³⁸. Another maker sets anode inspection intervals by hardness: for water with hardness at or below 250 mg/L CaCO3, two years after installation; above 250 mg/L CaCO3, or in critical or aggressive water, one year after installation, with subsequent inspections annually³⁹. In commercial installations where constant usage or reheat is required, titanium immersion heaters must be fitted to comply with the Mixergy warranty³⁸.

The practical point for a household is that the water supplied to the property, which is outside the household's control, can decide whether a 25-year warranty survives. A hardness test before purchase is the only way to know which side of the threshold a postcode falls.

Warranty and registration: the 60-day deadline and what keeps cover alive

Cylinder warranty periods are long and the conditions are strict. Mixergy warrants the stainless steel cylinder, the inner vessel including the sensor strip, for 25 years with registration via its warranty registration form, excluding labour; registration must be completed within 60 days of commissioning or of first legal completion of the property⁷. Under the earlier terms the cylinder carried 25 years from installation and the components 3 years from the date of installation³⁸. The homeowner guide states Mixergy X and Mixergy Solar X cylinders carry 25 years on the cylinder and 3 years on the components²², and the iHP X heat pump unit an initial 5-year warranty¹⁸.

The conditions matter more than the headline number. Mixergy's current terms require installation by a competent person in accordance with current UK Building Regulations and Mixergy's instructions, a completed and retained Benchmark commissioning checklist, an annual service carried out and documented either in the installation manual or supported by proof of payment from the servicing installer, and a servicing engineer registered with an appropriate competent person scheme such as Gas Safe Register where applicable⁷. Cover applies to products installed in the United Kingdom; products installed outside the UK and installations not carried out to the instructions are excluded, as are consequential losses including property damage or loss of earnings⁷. Vaillant requires installation and commissioning by a Building Regulations Approved Document G(3) qualified installer within 6 months of despatch of the cylinder from its warehouse, and its guarantee is subject to the laws of England and Wales with disputes heard before a court or tribunal in England⁴⁰.

The earlier Mixergy terms invalidate cover if the cylinder has been subject to frost damage, misused, tampered with, subjected to neglect, or modified in any way other than by Mixergy³⁸. Nothing on the warranty page affects statutory rights⁷. General guidance on this sits on manufacturer warranties and registering a warranty.

Making a claim: what to have ready

Mixergy Ltd takes warranty claims on 01865 595 875, weekdays 09:00 to 17:00, and asks for the product MX number, proof of installation and service history, and photographs with a description of the issue⁷. A valid claim is settled by a like-for-like replacement cylinder, or by replacement of the covered components as applicable, and the warranty covers replacement only: labour costs associated with replacing the cylinder or its components are not covered, and only replacement items are offered, not the cost of installing them³⁸. The defects covered are corrosion, material defects and manufacturing faults⁷.

The paperwork that supports a claim is created at handover, not afterwards. An installer should provide a commissioning checklist and hand over all documentation including the manufacturer's installation manual, warranty registration details, and a record of the safety valve settings²⁷. Homeowners are advised to keep proof of annual maintenance⁴². Where that paperwork is missing, the building control notification made at installation, or the competent person scheme record where the engineer was registered, may be the only surviving evidence of the date²⁷.

Regulations and servicing: G3, Benchmark and the annual visit

Two regimes bear on a stored hot water system. Building Regulations Part G3 governs unvented installation and competence, as set out above. Benchmark governs the record: it 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 products⁴³, and its purpose is to ensure that customers are provided with the correct products for their needs and that those products are installed, commissioned and serviced in accordance with the manufacturer's instructions by competent persons, safely, at optimum efficiency and meeting the appropriate Building Regulations⁴⁴. It is described elsewhere as a scheme promoting best practice in installation, commissioning and servicing of domestic heating and hot water systems⁴⁵.

Annual servicing is close to universal as a warranty condition. Unvented cylinder servicing validates the manufacturer's warranty and, in the maker's words, guarantees the cylinder operates efficiently in compliance with industry guidance and Building Regulations¹¹. One service checklist states plainly that to validate the warranty the cylinder must be serviced annually by a suitably qualified service engineer⁴². Making annual servicing a condition of the hot water cylinder warranty has been described as going some way to addressing the problem of unserviced stored water systems⁴⁶. Where a hybrid system is installed, manufacturers recommend annual servicing of hybrid units, which require both gas and electrical skill⁴⁷.

The industry itself considers the regulation dated. The Heating and Hotwater Industry Council has said it believes heat pumps should have a mandatory annual service, and has recommended a review of Part G3 of the Building Regulations, which it believes to be out of date and not reflective of the requirements for heat pump systems⁴⁷. It also argues the Benchmark service record is a means of maintaining high quality installation standards which would help maintain necessary noise requirements of heat pump installations⁴⁷. Separately, a heat pump installation must be notified to the distribution network operator within 28 days⁴⁸. Cylinder settings should be set by a boiler engineer and kept hot enough to avoid the build-up of bacteria in the storage tank⁴⁹.

Service cover for cylinders is also sold as a maintenance plan: published plans cover an unvented hot water cylinder and installation pipework in a heat-pump system, or an air-source heat pump plus unvented cylinder and the pipework for both⁵⁰. Plumbing firms list unvented cylinder installation and maintenance as a service line⁴⁶. More on this sits under manufacturer service plans.

The Hot Water Association and the case for stored water

The Hot Water Association is a trade organisation whose membership accounts for nearly 100% of hot water storage devices sold in the UK⁴⁶. It is the body behind much of the servicing guidance the manufacturers point to, and it has worked with the Chartered Institute of Plumbing and Heating Engineering on a webinar providing information and guidance on energy storage potential, grid enabled hot water stores and other thermal energy storage mediums⁵¹. That framing, the cylinder as a thermal battery, is the industry's principal argument against instantaneous combi supply.

The argument has substance for a self-sustaining household. A cylinder can be charged when electricity is cheapest or when a solar array is exporting, and newer cylinders can hold that heat for up to 48 hours²⁹, so the draw at the tap is separated from the draw on the grid. A cylinder can take heat from a heat pump, a solar thermal collector or an immersion heater, and some makers control how much of the volume is heated: Mixergy's patented top-down heating design is described as giving complete control over how much hot water is used²². Kensa states that heat pump cylinders deliver hot water whenever it is needed¹⁷.

The limits are equally real. A cylinder holds heat, not electricity, and cannot return energy to the grid¹. It takes floor space, more so with solar³³. It has to be raised above 60°C regularly for legionella control⁸, which costs energy that instantaneous heating does not. It carries a servicing obligation every year for the life of the warranty. And the smart models add a dependence on the manufacturer's platform: Mixergy's annual service condition can be evidenced by a Benchmark service record or by subscription to the Mixergy Care Plan or Care Plan Plus with annual monitoring via the online analytics platform³⁸. That is a commercial relationship lasting as long as the cover, which is an aspect of independence a household should weigh alongside the energy case. The wider question is set out on manufacturers and household energy independence.