BT Digital Voice (DV)

The impartial information on this page is given free of charge and without prejudice
It is accurate at the time of writing and may change over time - always check with BT or your provider

BT Digital Voice
Fault Finding

This page only deals with BT Digital Voice but some of the information is applicable to other line providers.

Overview
Digital Voice will be presented in three ways depending on your contract:-

Fibre to cabinet or premises with no internet connection. This is a telephone line supply only.
Fibre to premises with internet connection. The fibre directly feeds your premises and terminates on a white box called a Optical Network Termination Device (ONT)
Fibre to the cabinet with internet connection. The external feed is still copper wire and terminates on a data Network Connection Point.

In all the scenarios above a Smart Hub 2 is fitted and the telephone line is presented on the rear of hub on a green socket. The hub is also a DECT device so can support wireless telephones.

Fault finding is much reduced because BT or your supplier own most of the equipment.

Fault Finding

Smart Hub 2

Telephone and/or internet do not work
Firstly look at the front of the Smart Hub 2, it should have a blue light showing. If there is no light then check the mains supply at the socket. The hub is connected to a power block and the plug that connects it to the hub can easily fall out from the back of the hub (design fault).

If the power is good then check the colour of the light on front of the Smart Hub. The table below is supplied by BT and explains what the colours mean and what actions you can take:-

Light status	What it means	What to do
Blue	Your Hub is connected to your broadband ok	If you can't get online, it might be your device. Try switching your device off and on.
No light	The power is off or the lights have been turned off using the Hub Manager	Full Fibre connection Make sure your Openreach modem is connected to the mains and all the lights are on. Fibre connection Check that the Hub is plugged in, switched on and that its lights haven't been turned off in the Hub Manager. If this doesn't fix your issue, contact us.
Green	Your Hub is starting up	Wait for at least three minutes for it to turn blue. If it stays green, turn your Hub off and on again. If the light still doesn't turn blue, use a paper clip to press your Hub's factory reset button. If this doesn't fix your issue, please contact us.
Flashing orange	Your Hub is connecting to broadband	Give it at least three minutes to connect. The light will turn blue when your Hub is ready.
Flashing purple	Your Hub is working but the broadband cable isn't connected	Full Fibre connection Check the Ethernet cable (red ends) is plugged into the modem's PORT correctly. Then check the other end of the Ethernet cable is plugged into the WAN port of your Hub correctly - you'll hear a click. Fibre connection Check if the broadband cable (grey ends) is plugged incorrectly. And if you're using a filter, check that's plugged incorrectly too.
Orange	Your Hub is working but isn't connected to the internet	Connect a device to your Hub. Open a new web browser window and follow the on-screen help wizard to get connected.
Red	There's a problem somewhere	Using the Power button, turn your Hub off and on again. If the light still doesn't turn blue, use a paper clip to press your Hub's factory reset button. If this doesn't fix your issue, please contact us.
Purple	Your Hub is connected to the EE mobile network via Hybrid Connect	This may be because your broadband connection isn't set up yet, or because there's an issue with your broadband.
WPS button flashing	Used to connect DECT handsets	If it's flashing blue, it's waiting for you to press the WPS button on your computer or device (you've got two minutes). If it's flashing red, it didn't connect - give it a couple of minutes and try again.

If the hub has a blue light then check if the the WiFi is working. Use a mobile phone or WiFi device and check if your Hub can be seen. The WiFi SSID name will be on the rear of the Hub. If WiFi is available then try logging into the hub as detailed below.

A PC with a LAN cable can also be directly connected into the rear of the hub.

You can also try logging into the hub. Using a device (PC, smart phone etc) type into the address bar the following numbers including the full stops - 192.168.1.254 return. You should get a login screen appear and the details on logging in are also on the rear of the hub. The details are on a piece of plastic which will slide out so you can view the details next to your device.

Telephone does not work
At this point the assumption is that the Hub has a blue light and that the internet is working (if you pay for it).

A quick test is to connect a known working telephone into the green socket on the rear of the hub. If you get dial tone then the BT side is working. If it is dead then contact BT or your supplier.

If you are using the BT supplied DECT telephones - are they fully charged and do they show connected on their displays.

You can also log into the hub and see what DECT telephones are connected. You can connect with a smart mobile phone via WiFi or with a PC connected directly into the hub with a LAN cable.

Using a device (PC, smart phone etc) type into the address bar the following numbers including the full stops - 192.168.1.254 return. You should get a login screen appear and the details on logging in are also on the rear of the hub. The details are on a piece of plastic which will slide out so you can view the details next to your device.

Once logged in, on the home page is a telephone section with your phone number showing. Click on this to open the section. It will show all BT supplied DECT handsets/adaptors that have been registered and should say 'Service Ready' in Status. The Smart Hub 2 only supports five DECT telephones.

Modem or Optical Network Termination Device (ONT)
These are used on fibre to the premises installations and is a BT wall box which contains the incoming fibre optic cable and the cable that connects to the Smart Hub 2.

There are now (as of 9/6/2025) ONT types used by Openreach.

All these ONT's have lights on the front, click here for the meaning of these lights.

Huawei 1-port
As of 2024 these ONT's are no longer installed.

The Huawei 1-port model is also powered by a white coloured power supply which is connected to the battery unit (BBU).

The Smart Hub is connected to the ONT socket marked PORT 1 with the red plug needed cable. The other end of this cable is connected to the WAN port (Port 4) on the Smart Hub.

To access this gain access firstly open the door at the bottom of the unit. This door is hinged on the left and opens by pulling the tab on the right hand side. The top cover is fixed by a single Philips screw which will now be visible. It is to the right and just under the top door - you can see the screw hole in the picture. With the screw removed the cover will require a good pull to open.

The ONT box houses two units. Left is the fibre termination unit and to the right is a battery pack. The fibre terminating unit has 5 LED's and the battery pack has 3 LED's.

Normally no action is required with this box but sometimes a red fault light shows even though the phone and internet are working.

This normally happens after a power failure. Inside the battery pack are a couple of batteries. These batteries will be at a low voltage after a power outage and will start recharging. As they charge the red light will extinguish and the charging light will go yellow and then go out when they are fully charged. If the red fault light persists after 24 hours and then the batteries will require replacing. This is the customers responsibility according to BT.

The green optical cable would have been connected by your engineer. Do not unplug it. If the PON light is off and the LOS light is red or flashing, check that the cable's inserted fully into the modem.

Contact BT if you're still having issues and:-

The green optical cable is fully inserted.
or
The PON light is flashing and the LOS light is off.

The Battery Unit (BBU) has three LEDs which will indicate the status of the battery pack. These are at the bottom right of the BBU.

LED status explanation:-

STATUS	Solid green		Good
STATUS	Off
FAULT	Solid red	Battery fault	Bad. Replace the AA batteries inside
FAULT	Off		Good. No fault
CHARGING	Solid orange	Batteries are not fully charged	Wait, the batteries are charging (usually after a power cut)
CHARGING	Off	Batteries are not being charged	Good. The batteries are fully charged

Huawei 1+1 ONT

Battery Replacement
The battery pack is shown to the top right in the picture above, with the fibre terminating unit on the top left. The cover consists of two parts which are hinged on the left. The bottom the cover opens by just pulling on the right hand side side.

Before working on the battery unit ensure that the power is switched off or the power supply cable disconnected (pull down). Also disconnect the cable on the extreme left of the terminating unit (pull down).

The top cover is fixed by a single Philips screw which will now be visible. It is to the right and just under the top door - you can see the screw hole in the picture. With the screw removed the cover will require a good pull to open.

With the both covers open, the battery unit can be seen to the right. Slide the battery unit upwards and lift off the locators. On the rear of the battery box is a slide cover, which once removed exposes the four AA batteries. Unsure they are replaced with the same rechargeable type. Do not, under any circumstances, use ordinary AA batteries.

Some older units will have an external battery box (before April 2019).

An alternative to replacing batteries is to remove the Battery pack in its entirety and plug the power cable directly into the left hand termination unit.

BT advise that the battery backup unit uses four 2000 mAH-NiMH BYD rechargeable AA batteries at 1.2V.

This YouTube video shows how

Huawei 4-port
As of 2024 these ONT's are no longer installed.

This modem has four ports and the Smart Hub is connected to PORT 1.

Contact BT if you're still having issues and:-

The green optical cable is fully inserted.
or
The PON light is flashing and the LOS light is off.

ECI Modem
As of 2024 these ONT's are no longer installed.

ECI C-Series Modem
As of 2024 these ONT's are no longer installed.

Nokia Modem
The power requirements for this modem (Model G-010G-Q) is 12.0v DC at 0.5A. The power supply has a rated output of 12v DC at 0.5A (6 Watts).

The 1G model has a yellow Ethernet port, whilst the 2.5G model is coloured Orange. These ports connect to the Smart Hub.

Dimensions
82mm L x 89mm W x 27mm H.

Adtran SDX 611B/D (1G) and SDX 611Q (2.5G) ONT's
These ONT's are generally installed in a shroud type holder.

Dimensions
SDX 611B/D - 90mm L x 80mm W x 33mm H.
SDX 611Q - 78mm L x 78mm W x 24mm H.

Adtran SDX 611Q

LED Status Lights
A working Openreach unit will have green LED's as follows: power, PON & LAN lights, anything else indicates a problem.

The following table will assist in fault finding on a BT ONT.

Light	Status	Meaning	What to do
POWER (right-hand light)	Green	Openreach fibre modem is on.	Check PON and LOS status below.
POWER (right-hand light)	Off	Openreach fibre modem is off.	Check the mains plug is in.
PON and LOS (left-hand lights)	PON solid green	Fibre optic link to BT exchange is working and recognises your Openreach fibre modem.	Check physical connection at both ends of the cable between the Openreach fibre modem and Hub. Try new cable if needed.
	PON flashing and LOS off	Openreach fibre modem is communicating with BT exchange for verification.	Wait until light turns solid green.
	PON off, or PON and LOS both flashing	Fibre optic link is not connected or there's a problem between your property and the BT exchange.	Check that the thin white fibre optic cable coming into your Openreach fibre modem is inserted and not damaged. Turn the Openreach fibre modem's power off, then back on and wait five minutes for the Openreach fibre modem to attempt to reconnect.
PORT1-PORT4	On (any)	Ethernet connection is normal between Openreach fibre modem and Hub (Port 1 is where engineer will install).	There may be a connection problem - check your Hub.
	Blinking (any)	Data is being transmitted through the port.	There may be a connection problem - check your Hub.
	Off (all)	Ethernet cable to Hub is not inserted or broken.	Check physical connection at both ends of the cable. Try new cable if needed.
TEL 1-2	On (any)	The fibre home phone line is live on your modem.	Initially, you need to activate your fibre home phone line.
	Blinking (any)	Fibre home phone line is not activated.	Wait until light turns solid green.
	Off (all)	Fibre home phone line is not activated.	Check the mains cable is plugged in and the modem is switched on.
Optical	Green solid	Connected	Check physical connection at both ends of the cable between the Openreach modem and Hub. Try a new cable if needed.

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BT Digital Voice (DV)

Last revised: June 10, 2025