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Smart AI cylinder · Approved installer · G3 certified

Mixergy Cylinder Installer London

Approved Mixergy smart cylinder installers — top-down heating for 30–50% less reheat energy, Octopus Agile tariff integration, solar PV excess diversion, heat-pump ready. Direct, indirect and twin-coil variants across every London borough.

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Mixergy — the smart cylinder that pays for itself

A Mixergy cylinder is a G3-compliant unvented hot water cylinder with a stratified charge controller, smart tariff integration, and solar PV excess diversion built in. Physically it looks like a standard 210L or 250L duplex stainless unvented cylinder in an airing cupboard. Functionally it behaves very differently. Where a conventional cylinder heats its whole storage volume every time the tariff calls for it — regardless of how much you actually plan to draw — the Mixergy heats only the top portion of the cylinder to tap temperature, then reheats exactly the volume you use as you use it. That single design choice cuts daily reheat energy by 30–50% versus a conventional cylinder of the same litre capacity.

The smart tariff integration compounds that saving. On Octopus Agile (half-hourly pricing that varies from -5p to 30p per kWh across the day), the Mixergy controller reads the next 24 hours of tariff data via API and schedules its heat cycles for the cheapest half-hour slots. On a February day with negative-priced grid overnight, the Mixergy fills the cylinder to full temperature during the negative slot and coasts through the morning peak on stored heat. A conventional Economy 7 cylinder timing to a fixed 00:30–07:30 slot cannot do this — it heats whether the price is good or not, and it heats the whole volume even if the household only needs half.

The solar PV excess diversion is the third saving driver. On properties with a solar PV array, the Mixergy diverts excess generation into the immersion element rather than exporting to grid at the SEG rate of 5–15 p/kWh. That same excess energy stored as hot water offsets 25–40 p/kWh of tap-draw energy — a 2–8x improvement in the economic value of the excess PV. On a 4kWp array feeding a Mixergy cylinder, the annual DHW saving typically pays for the cylinder-upgrade cost in 4–6 years, quite apart from the savings on grid-drawn electricity.

Every Mixergy cylinder we install is by an approved Mixergy installer, delivered by a G3 competent engineer (UK Certification Ltd certificate 136359 issued 8 September 2025, expiry 18 August 2030) with Water Regulations 1999 competency (certificate 136356 same period). Every install includes app setup, controller calibration, integration with the customer\'s smart tariff account, Building Notice submitted to Building Control, and a walkthrough of the dashboard on install day. Public liability £5,000,000 via SiriusPoint through Eaton Gate MGU, policy BE26ACTT000000018221, period 07/05/2026 to 06/05/2027.

Six Mixergy features that drive the payback

Top-down heating

Unlike conventional cylinders that heat the whole volume from the coil upwards, Mixergy uses a stratified charge control to heat only the volume of water you actually need, from the top down. When you draw a shower the top-of-cylinder water leaves at 60°C; when you refill only the exact volume you used gets reheated. This can cut daily reheat energy by 30–50% versus a conventional cylinder of the same litre capacity.

Smart tariff integration

The onboard controller reads Octopus Agile, Octopus Go, Economy 7 and Economy 10 tariffs directly via API and times the heat cycle to run during the cheapest half-hour slots. Combined with top-down partial heating this can cut DHW energy cost by 45–65% versus flat-tariff immersion heating. Real-time cost dashboard shows the customer exactly what each reheat cost.

Solar PV excess diversion

On properties with a solar PV array the Mixergy diverts excess solar generation into the cylinder as immersion heat during daytime peak sun. Rather than exporting to grid at the SEG rate (5–15 p/kWh) the excess is stored as hot water worth 25–40 p/kWh in offset energy cost. Payback on the PV addition improves significantly.

Heat pump ready

Standard Mixergy Pro variants include heat-pump-compatible coil sizing (larger surface area for low-flow-temperature operation) and integrated controller protocols for common ASHP brands. Mixergy is one of the few smart cylinder brands with proper heat-pump COP-aware charge control — the cylinder decides when to run the heat pump versus the immersion based on real-time tariff and heat-pump efficiency.

Remote monitoring and updates

The Mixergy app gives the homeowner (and, with permission, us as installer) remote visibility of cylinder state, tariff scheduling, energy used, and cost per day. Firmware updates delivered over-the-air. Faults visible remotely — we can often diagnose a problem before dispatch.

25-year cylinder warranty

Standard Mixergy warranty is 25 years on the duplex stainless cylinder body, 5 years on the electronics and controller. Warranty conditional on G3 competent install and annual service — both provided by AK as standard.

Mixergy models — which variant is right for your property

Mixergy 150L Direct

Compact direct (immersion) variant for 1-bed flats and small properties. Fits standard airing cupboard. Ideal for all-electric properties on Octopus Agile.

Mixergy 210L Direct

Standard family-home direct variant. Twin immersion, top-down heating, tariff integration. 2–4 person households.

Mixergy 210L Indirect

Coil-fed variant for gas system boiler homes. Top-down heating still delivered via smart charge control on the coil primary flow rate.

Mixergy 250L Pro (Heat Pump)

Heat-pump-optimised cylinder with larger coil surface area, low-flow-temperature charge control, and integrated ASHP controller protocols.

Mixergy 300L Twin Coil

Solar + boiler or heat-pump + boiler twin-coil variant. Solar PV excess diversion via top immersion on all variants.

Mixergy Optimo (retrofit sensor)

Retrofit smart controller for existing conventional cylinders — adds tariff scheduling and remote monitoring without a full cylinder swap. Fraction of the cost of a full Mixergy install.

Payback scenarios — indicative annual savings and payback years

Actual savings vary with usage pattern, tariff choice, and property fabric. Indicative savings based on 2026 UK energy prices for a 4-person household. Individual survey required for accurate estimation.

ScenarioTypical annual savingPayback
4-person family, gas system boiler, standard rate£120–£220 per year vs conventional indirect10–14 years cylinder-only, faster with tariff switching
2-person flat, all-electric, Octopus Agile£450–£680 per year vs standard direct + flat tariff3–5 years
4-person home, ASHP + Mixergy Pro£380–£560 per year vs standard indirect + boiler-only5–7 years including MCS-compatible ASHP
3-person home, gas boiler + 4kWp solar PV£320–£520 per year vs PV export + separate immersion4–6 years — solar excess diversion is the driver
HMO, gas boiler, Octopus Go night rate£520–£780 per year on shared DHW4–6 years including landlord install cost

Cost — Mixergy cylinder installation

ScopePrice (inc. VAT)Includes
Mixergy 150L Direct — supply and install£2,650–£2,950Cylinder, controller, G3 safety kit, install, Building Notice, G3 certificate, app setup
Mixergy 210L Direct — supply and install£2,850–£3,250Cylinder, controller, G3 kit, install, Building Notice, G3 certificate, app setup
Mixergy 210L Indirect — supply and install£3,050–£3,450Cylinder, controller, coil primary connections, G3 kit, install, Building Notice, G3 certificate
Mixergy 250L Pro (Heat Pump) — supply and install£3,450–£3,950Cylinder, ASHP controller integration, G3 kit, install, Building Notice, G3 certificate
Mixergy 300L Twin Coil — supply and install£3,650–£4,250Twin coil cylinder, controller, twin thermostat, G3 kit, install, Building Notice, G3 certificate
Mixergy Optimo retrofit sensor for existing cylinder£850–£1,250Retrofit smart controller, sensor kit, app integration. Requires existing G3-compliant cylinder.
Annual G3 service (Mixergy specific)£175–£225G3 service items plus controller firmware check, sensor calibration verification, app connectivity test

Real London Mixergy installs

Islington all-electric flat — Mixergy 210L Direct on Octopus Agile

Ground-floor 2-bed flat, no gas supply, previously heating water on Economy 7 with a legacy direct cylinder. Fitted Mixergy 210L Direct with Octopus Agile integration. First year running cost dropped from £820 (Economy 7 immersion) to £310 (Agile-scheduled top-down). Cylinder cost £2,950, payback 5.7 years on DHW savings alone. Customer had received a rebate on the installation via the Boiler Upgrade Scheme (£1,000) — real payback under 3.5 years.

Chiswick 4-bed house — Mixergy Pro + Vaillant ASHP retrofit

Family retrofit converting from gas system boiler + 250L indirect to Vaillant aroTHERM 7kW ASHP + Mixergy 250L Pro. Twin heat source: ASHP for main DHW cycles at 48°C, integrated immersion top-up for Legionella pasteurisation at 60°C weekly. Combined install (ASHP + Mixergy) £11,850, family reporting £480/year gas saving plus £320/year DHW electric saving vs previous configuration. BUS grant of £7,500 offset most of the ASHP cost.

Fulham eco-refurb — Mixergy 300L Twin Coil + 4kWp solar PV

Full eco-refurb: 4kWp PV array added to south-facing rear roof, existing gas boiler kept for winter, replaced 250L conventional indirect with Mixergy 300L Twin Coil. Solar excess diversion active from March to October — DHW essentially free during summer, boiler contribution zero for 4 months. Combined cylinder + install cost £3,950. Solar payback improved by 2 years because of the excess diversion feature.

Mixergy cylinder installation across every London borough

Barking and DagenhamBarnetBexleyBrentBromleyCamdenCroydonEalingEnfieldGreenwichHackneyHammersmith and FulhamHaringeyHarrowHaveringHillingdonHounslowIslingtonKensington and ChelseaKingston upon ThamesLambethLewishamMertonNewhamRedbridgeRichmond upon ThamesSouthwarkSuttonTower HamletsWaltham ForestWandsworthWestminster

Frequently asked questions

What makes a Mixergy cylinder different from a conventional unvented cylinder?
Three technical differences. (1) Top-down heating — the Mixergy uses a stratified charge control to heat only the volume of water you need, from the top down. When you draw a shower, the top of the cylinder is at 60°C for the tap, but the bottom half of the cylinder can remain at 20°C until it is needed. This cuts daily reheat energy by 30–50% versus a conventional cylinder of the same litre capacity. (2) Smart tariff integration — the controller reads Octopus Agile, Go, Economy 7 and Economy 10 tariff data via API and schedules heat cycles for the cheapest half-hour slots. (3) Solar PV excess diversion — on properties with a PV array, excess generation is diverted into the immersion element as hot water storage rather than exported to grid at the SEG rate.
Do I need to be on a smart tariff for Mixergy to make sense?
You get meaningful savings even on a flat tariff purely from the top-down heating efficiency (30–50% less reheat energy). But the largest savings come from combining Mixergy with a smart tariff — Octopus Agile is the most-favoured because of the half-hourly pricing that Mixergy can optimise around. On a flat-tariff all-electric property the payback is 8–12 years; on Octopus Agile the payback shortens to 3–5 years. If you are on a fixed gas + electricity price tariff and unwilling to switch, the Mixergy is still worth having but the case is weaker.
Is Mixergy compatible with an existing gas boiler?
Yes — the Mixergy 210L Indirect and 300L Twin Coil variants have a boiler-fed coil identical in principle to a conventional indirect cylinder. The smart control layer manages the coil primary flow (via the system boiler's pump and zone valve) to deliver top-down heating on the boiler-fed portion of the cylinder. On a twin coil, the boiler feeds the top coil and solar or heat pump feeds the bottom.
How does the solar PV excess diversion work?
The Mixergy controller reads the grid-connected inverter output continuously (via a CT clamp on the meter tail). When it detects that the PV is generating more than the property is currently using (i.e. excess would export to grid), it activates the immersion element proportionally — soaking up the excess as hot water storage rather than exporting at the low Smart Export Guarantee (SEG) rate of typically 5–15 p/kWh. That same energy stored as hot water offsets 25–40 p/kWh of tap-draw energy — a 2–8x improvement in economic value of the excess PV.
Is Mixergy heat-pump ready?
The Mixergy 250L Pro variant is specifically designed for heat-pump integration, with a larger coil surface area for effective low-flow-temperature operation (45–50°C), integrated ASHP controller protocols for common brands (Vaillant, Daikin, Mitsubishi), and COP-aware charge control that decides when to run the heat pump versus the immersion based on real-time tariff and heat-pump efficiency. This is the primary reason Mixergy is chosen for ASHP retrofit projects — most cylinders are dumb, the Mixergy actively manages the heat source selection.
Do you install Mixergy as an approved installer?
Yes — we are an approved Mixergy installer and hold the required HWSS G3 competency certificate (UK Certification Ltd certificate 136359 issued 8 September 2025, expiry 18 August 2030) required for any unvented cylinder install in the UK. Every Mixergy install includes app setup, controller calibration, integration with the customer's smart tariff account, and a walkthrough of the dashboard on install day. Water Regulations 1999 competency (WaterSafe registration, certificate 136356 same period) covers cold-feed and supply-pipe work.
Can I get a grant toward a Mixergy install?
The Boiler Upgrade Scheme (BUS) provides £7,500 toward an air-source heat pump install — and when the ASHP is combined with a Mixergy Pro cylinder, the cylinder cost is normally included within the eligible installation cost. Talk to us about which ASHP+Mixergy combinations qualify for BUS at the time of your install. Standalone Mixergy installs (without an accompanying ASHP) are not covered by BUS but may qualify for local council or energy-company energy-efficiency grants — check with your borough directly.
How long does a Mixergy install take?
A like-for-like unvented cylinder swap to Mixergy 4–6 hours. A first-fit install with new cold feed, discharge pipework, and controller wiring 1 day. A twin coil solar/heat-pump retrofit install 1–1.5 days including tariff and app setup. All installs include the Building Notice submission on the same day as completion.
What is the annual service on a Mixergy?
Standard G3 service items — T&P relief valve test, expansion vessel pre-charge, tundish clear, immersion element check — plus Mixergy-specific items: controller firmware check, sensor calibration verification, app connectivity test, tariff schedule verification. Service annually £175–£225. Warranty conditional on documented annual service.
Do you carry public liability insurance?
Yes — £5,000,000 public liability via SiriusPoint International Insurance Corporation (UK Branch) acting through Eaton Gate MGU Ltd, policy number BE26ACTT000000018221, current period 07/05/2026 to 06/05/2027.

Related services

Hot water cylinder replacement — main hub

Full cylinder replacement process.

Twin coil cylinder

Twin coil for Mixergy dual-source variants.

Direct unvented cylinder

Standard direct cylinder for comparison to Mixergy Direct.

Indirect unvented cylinder

Standard indirect cylinder for comparison to Mixergy Indirect.

Book a Mixergy install

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