How to Plan a Solar Diverter Install: Step by Step (2026)
A solar diverter sends surplus solar power to your immersion heater instead of exporting it, giving you free hot water. Fitted cost is £200–£500 and payback is typically 2–4 years. The whole job takes 2–3 hours — but only if you have a hot-water cylinder. Here is the plan, step by step.
The Three Things That Decide If a Diverter Suits You
Get these right before you book anyone. A diverter is one of the cheapest solar upgrades available — but it is useless in the wrong house.
A diverter dumps surplus power into an immersion element. If you have a combi boiler with no cylinder, there is nothing to heat — a diverter cannot work.
If you already use most of what you generate, or have a battery soaking up the surplus, there is little left to divert and the payback stretches out.
On a high export tariff, selling the surplus can beat heating water with it. Compare your export rate against what you pay for the gas or electricity you would otherwise use.
Most solar installers fit diverters as a bolt-on, often while doing other work. Get quotes from vetted MCS-registered installers.
Get matched →Solar Diverter Costs 2026
| Item | Typical cost | Notes |
|---|---|---|
| Diverter unit | £150–£320 | Single-phase units; smart models with app monitoring sit at the top |
| Installation labour | £100–£220 | 2–3 hours for a qualified electrician |
| New immersion element | £90–£180 | Only if your cylinder has no spare or working immersion |
| Typical all-in fitted | £200–£500 | Cheaper if fitted alongside a solar or battery install |
Costs are UK averages for Q3 2026. Fitting a diverter at the same time as other solar work usually saves £80–£150 in labour.
The Six-Step Install Plan
Step 1 — Confirm you have a cylinder with a working immersion
Find your hot-water cylinder and check for an immersion element (a thick cable entering the side or top, usually with a red reset button). Many cylinders have two elements; a diverter can use the spare. No cylinder means no diverter — consider a battery instead.
Step 2 — Measure your actual export
Check your inverter app or smart meter data for a sunny week. If you are exporting 3–6 kWh a day in summer, a diverter will comfortably cover your hot water. Under 1–2 kWh a day and the payback stretches past five years.
Step 3 — Choose the right unit for your setup
Check the diverter is rated for your immersion (usually 3 kW) and matches your supply — three-phase homes need a three-phase-compatible model. If you have a battery, pick a unit that lets you set battery-charging priority so the battery fills before water is heated.
Step 4 — Plan the cable route and CT clamp position
The installer fits a current transformer (CT) clamp on the incoming supply tail at the meter, and runs a cable from the diverter to the immersion. The shorter and tidier that route, the cheaper the labour. Awkward routes through finished rooms are the main cost variable.
Step 5 — Book a qualified electrician (Part P)
This is notifiable electrical work under Part P of the Building Regulations. Use an electrician registered with a competent-person scheme such as NICEIC or NAPIT, or your solar installer. You should receive an electrical installation certificate on completion.
Step 6 — Commission and set your cylinder thermostat
Once fitted, watch the unit modulate power to the immersion as surplus rises and falls. Set the cylinder thermostat to 60 °C — hot enough to control legionella, without wasting surplus on unnecessary heat. Then reduce your boiler’s hot-water schedule so it stops heating water the sun has already heated. Skipping this last step is the most common reason people see no saving.
What a Diverter Actually Saves
A 4 kW solar array on a three-bed semi with a 180-litre cylinder and a gas boiler.
- Surplus diverted to hot water: ~750 kWh/yr
- Gas displaced (at 85% boiler efficiency): ~880 kWh of gas
- Gas saving at 2026 rates: ~£58/yr
- Export income given up (at 15p/kWh): −£113/yr
- Net result on a high export tariff: the diverter loses money
That last line matters. On a generous export tariff, exporting beats diverting when your backup is cheap mains gas. A diverter pays best when you have no export payment, a low export rate, or an electric-only water heating setup where the displaced energy costs 25p/kWh rather than 7p. In that case the same 750 kWh saves around £190 a year and a £350 install pays back in under two years.
Run your own numbers on your export rate before you commit — it is the single biggest factor and it is often ignored.
Solar Diverter Install — FAQ
Typically 2–3 hours for a qualified electrician on a straightforward job. The main variable is the cable route between the diverter and the immersion heater.
No. It involves a CT clamp on your incoming supply tails and a new circuit to the immersion, which is notifiable work under Part P of the Building Regulations. Use an electrician registered with a competent-person scheme.
Usually not as a priority. A battery captures surplus at higher value because that energy can run anything in the house, not just the immersion. If you already have a battery, only add a diverter for the surplus left over once the battery is full.
No. Combi boilers heat water on demand and have no cylinder or immersion element for a diverter to feed. You would need to install a cylinder first, which changes the economics entirely.
60 °C. That is hot enough to control legionella risk while avoiding wasted surplus on excess heat. Remember to cut back your boiler’s hot-water schedule so it does not reheat water the sun has already warmed.
Get Free Solar Diverter Quotes
BestBuilders matches you with up to 3 vetted MCS-registered solar installers who can fit a diverter, check your export data and tell you honestly whether it will pay back on your setup.
Get Solar Diverter Quotes — Free
Tell us about your solar system and hot-water setup. We will match you with up to four vetted installers who can price the install and confirm your expected saving.
Start your quote →