What Is an ONT Box? Fibre Broadband Equipment Explained (2026)

An ONT, or optical network terminal, is a small white box installed inside your home when you get FTTP broadband. It converts light signals travelling through the fibre optic cable into electrical signals that your router can use. The ONT connects to your router via an Ethernet cable and is typically mounted on a wall near where the fibre enters your property.

What an ONT Does and How It Works

The ONT is the bridge between the fibre optic network and your home network. Fibre optic cables carry data as pulses of light, but your router and devices communicate using electrical signals. The ONT performs this conversion instantly, allowing gigabit speeds to flow seamlessly from the outside network into your home. Openreach installs a standard ONT for all its FTTP connections, typically the Nokia or Huawei model measuring roughly 20 cm by 12 cm. BT, Sky and all other Openreach-based providers use the same ONT hardware, as it belongs to the Openreach network layer. The ONT has a single Ethernet port that connects to your router with a standard Cat5e or Cat6 cable. It also has an optical port where the fibre cable terminates, plus power and status LEDs. The ONT requires mains power via a small adapter, meaning it will not work during a power cut unless you connect it to a battery backup or UPS.

ONT Installation: What to Expect

When you order FTTP broadband, an Openreach engineer visits your home to install the ONT and connect the fibre cable. The visit typically takes one to two hours. The engineer will discuss the best entry point for the cable, usually through an existing duct or by drilling a small hole through an exterior wall. The ONT is then mounted on the wall near the entry point, ideally close to where you plan to position your router. Hyperoptic installs its own ONT in multi-dwelling buildings, often pre-wired into apartments during construction. Community Fibre similarly pre-installs in new-build London developments. You can request the ONT location during the engineer visit, but moving it later requires another appointment. The ONT is Openreach property and remains installed even if you switch providers, as the new provider simply reprovisions the same equipment. If you cancel FTTP entirely, Openreach may arrange to collect the ONT, though in practice it is often left in situ.

Common ONT Issues and Troubleshooting

Most ONT problems relate to power or the optical signal. If the ONT's power light is off, check the mains adapter and socket. A red or flashing optical light indicates a break in the fibre cable between the exchange and your home, which requires an Openreach engineer to repair. If your broadband drops but the ONT lights appear normal, the issue likely sits between the ONT and your router, so try replacing the Ethernet cable. Vodafone's Smart Hub connects directly to the Openreach ONT and runs automatic diagnostics if it detects a fault. EE's Smart Hub Pro also monitors the ONT connection and can alert you to issues via the EE app. The ONT itself rarely fails, with an expected lifespan of 10–15 years. If it does malfunction, your provider arranges a free replacement through Openreach under the automatic compensation scheme, which pays you £6.10 per day for loss of service beyond two working days.

ONT vs Router: Understanding the Difference

The ONT and router serve distinct functions. The ONT handles the fibre-to-electrical signal conversion and nothing else. It does not broadcast Wi-Fi, manage your network, or assign IP addresses. Your router handles all of those tasks, connecting to the ONT via Ethernet and creating the wireless and wired network your devices use. Some providers bundle a combined ONT-router unit for their own networks. Gigaclear and Toob supply integrated devices that combine both functions into a single box, simplifying the setup. For Openreach-based connections from providers like BT, Plusnet or Zen Internet, the ONT and router remain separate. If you prefer to use your own third-party router, simply connect it to the ONT's Ethernet port and configure your provider's connection settings. Wi-Fi 6 and emerging Wi-Fi 7 routers pair well with FTTP connections, as they can distribute gigabit speeds wirelessly across your home. The ONT imposes no speed limitation up to its rated maximum, typically 2.5 Gbps on current Openreach hardware.

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Frequently Asked Questions

Can I move my ONT to a different room?

Moving an ONT requires an Openreach engineer visit because the fibre cable must be rerouted. You can book this through your provider, though there may be a charge of £50–130 for the appointment. Alternatively, use a long Ethernet cable or powerline adapters to connect the router in another room.

Does the ONT use much electricity?

An ONT consumes approximately 10–15 watts, similar to a phone charger. Running continuously, it costs roughly £15–20 per year at current energy prices. It must remain powered on for your broadband to work, as the ONT has no battery backup unless you add one yourself.

Do all fibre providers use an ONT?

All FTTP providers require an ONT or equivalent device to convert the optical signal. Openreach, CityFibre, Hyperoptic, Community Fibre and other networks each install their own ONT. If you switch between providers using the same network, the existing ONT is reused.

What happens to the ONT if I switch provider?

If your new provider uses the same underlying network, the ONT stays in place and is simply reprogrammed. Switching from BT to Sky on Openreach, for example, keeps the same ONT. If you move to a different network entirely, a new ONT from that network would be installed alongside.

Related Guides

What Is FTTP Broadband? · Broadband Installation What to Expect · Broadband Router Guide · How to Set Up Broadband Router

Methodology & Sources

Information in this guide is sourced from Ofcom market reports, Openreach coverage data, ISPreview.co.uk, provider websites and independent broadband research from Point Topic and Thinkbroadband. Prices and availability are checked monthly. Speed data reflects advertised average speeds from provider Key Facts documents.