Best Solar Diverter UK 2026: Eddi vs iBoost and Which to Buy

If your solar panels are generating more than your home can use, that surplus goes to the grid at the Smart Export Guarantee rate — typically 3–15p/kWh. A solar immersion diverter intercepts that export and uses it to heat your hot water instead, at the value of avoided electricity (around 24.67p/kWh under the Ofgem Q2 2026 price cap). It is the cheapest and simplest upgrade a solar household can make. This review compares the two most popular models in the UK: the myenergi eddi 2.1 and the Marlec Solar iBoost+. For context on where a diverter sits versus a battery or EV charger, see our solar diverter vs battery vs EV charging guide.

How a solar diverter works

A CT clamp on your electricity meter senses export in real time. The diverter unit — wired between your consumer unit and your immersion heater — modulates the power sent to the heating element to match that surplus exactly. Rather than switching the immersion on and off crudely (which wastes power), modern diverters use phase-angle control or burst-fire control to throttle from near-zero up to the full 3 kW element rating in small steps. The result is that almost every watt of surplus solar heats water rather than spinning the export meter.

One important prerequisite: your home must have a hot water cylinder with an immersion heater element. Diverters are incompatible with combi boilers, which have no storage tank. Homes with a system boiler and a separate hot water cylinder, heat-pump cylinder, or all-electric cylinder are all compatible.

myenergi eddi 2.1

The eddi is the most feature-rich solar diverter available in the UK. It uses a wireless CT clamp (the Harvi sensor) to monitor grid import/export and adjusts power to the immersion in real time. Key features include:

• Dual-load support: the eddi can divert to two immersion heaters or switch between a second load such as a towel rail or underfloor heating element, cycling between them as configured.
• myenergi app and hub integration: the eddi connects to the myenergi Hub — a Wi-Fi bridge that also links any Zappi EV charger on the same property. From the app you can set priority (e.g. charge the car first, then heat water), view live energy flow, set boost timers, and receive firmware updates automatically.
• Zappi co-ordination: if you own or plan to buy a Zappi v2 EV charger, the eddi and Zappi communicate over the hub's 868 MHz RF link, sharing the solar surplus intelligently rather than competing for it. This is the eddi's most compelling advantage for households that have or expect an EV.
• Home Assistant support: via a community integration, the eddi exposes real-time data to Home Assistant for custom automations and dashboards. See our Home Assistant solar integration guide for more detail.
• Weather compensation: the app can optionally pull forecast data and pre-boost the cylinder on cloudy mornings if needed.

eddi price and installation

The eddi 2.1 unit retails for approximately £400–£430 from UK distributors such as CEF and Solar Trade Sales. Installed, expect to pay £550–£750 in total — the device plus an hour or two of electrician time (no G100 or DNO notification is required; a standard Part P competent electrician can install it). The myenergi Hub is sold separately at around £80–£100 and is optional unless you also have a Zappi.

Marlec Solar iBoost+

The iBoost+ is the UK's longest-established solar immersion controller, with over 125,000 units installed. It uses a wireless CT sender that clips to the meter tails to detect grid export; the sender communicates by 868 MHz radio to the iBoost+ controller, which is wired into the immersion heater circuit. The system is largely set-and-forget once installed. Key features:

• Buddy display: the optional iBoost+ Buddy (a small wireless monitor, sold separately for around £40–£50) shows live savings in £/hour, today's diverted kWh, and a traffic-light indicator for whether the home is currently exporting or importing. A practical addition for households that like a dashboard without needing a smartphone app.
• Two-immersion switching: the iBoost+ can wire to two immersion heaters simultaneously and switch between them automatically to maximise heating coverage.
• Proven reliability: the design has been stable for over a decade, widely adopted by UK solar installers, and supported by a straightforward warranty. Many installers are more familiar with the iBoost+ than any other diverter model.
• No app required: the iBoost+ has no smartphone app or cloud account. For households that prefer a simpler, self-contained device, this is a feature rather than a limitation.

iBoost+ price and installation

The Solar iBoost+ unit retails for approximately £250–£300 from UK suppliers such as Marlec directly and Electricpoint. Installed, expect to pay £350–£500 in total, making it noticeably cheaper than the eddi as a supply-and-fit package. Installation requirements are identical — no DNO notification, Part P competent electrician, same day job.

eddi vs iBoost+: head to head

Payback and savings

Both devices deliver essentially the same energy saving once installed — the difference is cost and features, not divert efficiency. Annual savings depend on how much surplus your array generates and what you currently pay for hot water. Typical UK estimates from industry sources:

• All-electric home (immersion as primary hot water source): saving around 13–17p per kWh diverted (avoided import minus forgone SEG export). A household with a 4 kWp array in southern England might divert 700–1,000 kWh/year, saving roughly £100–£170/year. At those rates, an iBoost+ pays back in under 4 years; an eddi in 4–7 years.
• Gas-heated home (immersion as backup): savings are more modest — you displace gas at around 6p/kWh rather than electricity. Payback periods lengthen considerably; assess carefully before buying.

Diverter payback is therefore most compelling for all-electric households or those moving toward heat-pump water heating, where avoided electricity costs are high.

Which should you buy?

Buy the myenergi eddi if: you own or plan to buy a Zappi EV charger; you want app control and remote boost timers; you use Home Assistant and want automation; or you want a three-year warranty and myenergi's ongoing ecosystem development. The price premium is worth it if the Zappi integration alone saves you manual juggling of solar surplus.

Buy the Solar iBoost+ if: you want the most proven, lowest-cost way to divert solar to hot water with no ongoing app or account dependency; your installer is already familiar with it (common for older installs and retrofit jobs); or you simply want a reliable set-and-forget device at the lowest installed price.

If you are also considering whether to use solar surplus for EV charging or home battery storage instead, our comparison of diverters, batteries and EV charging sets out the financial trade-offs in full.

Installation and compatibility checklist

• Hot water cylinder with a standard 3 kW immersion heater element — required for both devices
• No combi boiler (combi boilers have no storage cylinder)
• Space near the consumer unit for the controller (both units are compact wall-boxes)
• No G100 DNO notification required — a Part P competent electrician can install and certify
• Wireless CT sender needs line-of-sight or clear wall path to the controller (up to 30 m for iBoost+; eddi uses Harvi which also clips to meter tails)