Helpful video reference. We use Marlec's official "Solar iBoost+ Installation Guide" as the video reference here. Marlec are the UK manufacturer of the Solar iBoost, and their guide covers the full installation process including CT clamp placement and immersion heater wiring in a UK domestic setting.
1. Understand what a solar PV diverter does
When your solar panels generate more electricity than you are using at that moment, the surplus would normally flow back to the grid. With a diverter fitted, a current transformer (CT) clamp on the incoming supply detects this surplus and triggers the diverter unit to send that energy to your immersion heater instead.
The result is free hot water on sunny days. Popular units in the UK include the Solar iBoost+ (by Marlec, Rutland) and the Myenergi Eddi. Both work with standard 3 kW single-element or twin-element immersion heaters in vented or unvented cylinders.
Diverters are not storage. They work in real time only. If you want to charge a battery or run other appliances from surplus solar, you need a different device such as the Myenergi Zappi (for EV charging) or a battery inverter.
2. Check your home is suitable
You need all three of the following before a diverter makes sense:
- An existing solar PV array that is generating and connected to the grid.
- A hot water cylinder with an immersion heater element (vented or unvented).
- A dedicated immersion heater circuit from the consumer unit, or a fused connection unit already in place.
Combi boilers have no stored cylinder, so there is nothing for the diverter to heat. If you have a combi, a diverter will not work for you. Homes with a system boiler and separate cylinder are fine.
Check the immersion heater thermostat is set no higher than 60 degrees C. The diverter will heat water to thermostat cut-off, which is what you want, but an overtemperature in an unvented cylinder can trigger the thermal cut-out.
3. Choose the right diverter unit
Most domestic immersion heaters are 3 kW single-phase, so any standard UK diverter will cope. If you have a twin-element cylinder (day and night elements), confirm which element the diverter will connect to. Typically the top (day) element is wired to the diverter and the lower (off-peak/economy) element stays on its existing circuit.
If your property has a TT earthing arrangement (an earth rod rather than a PME supply), check the manufacturer's specification before ordering. Some diverters have earthing requirements that differ between TN-C-S and TT systems.
4. Position the diverter unit near the cylinder
The main diverter box mounts on a firm wall, typically inside the airing cupboard alongside the hot water cylinder. It needs to be within reach of the immersion heater flex and the incoming supply. Allow the clearances stated in the installation manual on all four sides for ventilation.
The Sender unit (which houses the CT clamp connection) mounts separately near the electricity meter or consumer unit. These two units communicate wirelessly on most models, so cable runs between them are not normally required.
5. The electrician fits the CT clamp at the meter
This is the step that requires a qualified electrician. The current transformer (CT) clamp sits on the live incoming supply cable between the meter and the consumer unit, known as the meter tails. Opening the meter enclosure is a network operator task, but fitting the clamp on the visible section of tails inside your consumer unit enclosure is work your electrician can carry out.
The CT clamp is a split-core type: it clips around the cable without cutting it. The orientation matters, and most manufacturers supply an indicator on the clamp to show which direction detects export. Getting this backwards means the diverter activates when you are importing (wasting energy) rather than exporting (saving it).
6. Wire the diverter to the immersion heater circuit
The electrician isolates the immersion heater circuit at the consumer unit, confirms it dead with a voltage tester, and then wires the diverter in-line between the existing circuit and the immersion heater element. On most units this means connecting the incoming supply to the Line In / Neutral In terminals and the immersion heater flex to the Line Out / Neutral Out terminals.
The earth conductor connects directly through and is not switched by the diverter. All connections must be made to the correct terminals with the right conductor sizes, typically 2.5 mm² or 4 mm² T&E cable matching the existing immersion circuit.
7. Commission and test the system
With power restored and the solar array generating, the diverter display will show whether it is detecting grid export. On a bright day you should be able to confirm the immersion heater is drawing power when the panels are generating more than your home is consuming.
On the Solar iBoost+ you can check the accumulated energy diverted on the display. On Myenergi units the Eddi app shows real-time and historic data once paired via the hub.
The electrician must issue a Minor Works Certificate or an Electrical Installation Certificate for this work. Keep this with your solar installation documentation.
When to call us
The full installation, including CT clamp fitting and immersion heater circuit connection, is a job for a registered electrician. Richard covers Sandwich, Deal, Dover and east Kent, and is familiar with both Solar iBoost and Myenergi Eddi installations alongside EV charger and battery storage work.
Installing a solar diverter in east Kent?
Richard can assess your existing solar setup, specify the right diverter, and complete the installation with the Part P certificate included.
Contact Richard