topic Re: ONT LAN light appears only briefly after power cycle of ONT in Full Fibre

ONT LAN light appears only briefly after power cycle of ONT

scott_doyland — Sat, 02 May 2026 11:47:09 GMT

Hi,

A few years ago I had an ONT fitted.

However, it is not in use yet as I am still using my phone line for my internet.

I want to swap to full fibre but there seems to be an issue with the ONT.

I have tested with two ethernet cables connected to the WAN port on my router, and with two laptops (connected the ONT LAN to the laptops).

In each scenario the ONT LAN port comes on for ~5 seconds during a power cycle, then goes off permanently. I am 99% sure that when it was first installed, the LAN port was solid green when I tested it.

I think the LAN port should be solid green when a powered on device is connected to it.

Therefore, following all my tests, I think the ONT is faulty.

Can this be replaced before I ask to swap to full fibre please.

Thanks,

Scott

Re: ONT LAN light appears only briefly after power cycle of ONT

KeithFrench — Sat, 02 May 2026 12:03:13 GMT

It should flash in line with data activity. If you connect an Ethernet-connected device directly to the LAN port of the ONT, what does the light do then?

Re: ONT LAN light appears only briefly after power cycle of ONT

scott_doyland — Sat, 02 May 2026 12:18:53 GMT

It does exactly what I said in my original post 🙂

If I attach the router, or laptop directly, the LAN light comes on briefly when I power cycle the ONT, then it goes off permanently.

The LAN light should stay on permanently when a device is attached, and flash on/off quickly when there is data transfer.

Can one of the TalkTalk mods please reply - I think the ONT is faulty and needs replacing.

Re: ONT LAN light appears only briefly after power cycle of ONT

KeithFrench — Sat, 02 May 2026 12:21:01 GMT

This will require TalkTalk to organise this. There are no TalkTalk support staff on this forum anymore.

Please see my signature for TalkTalk contact methods.

Re: ONT LAN light appears only briefly after power cycle of ONT

fr8ys — Sat, 02 May 2026 12:51:39 GMT

@KeithFrench if the ONT is not in use so no internet, would this affect what the ONT lights show as no data transference?

Agree the customer needs to contact TalkTalk direct though, but wondered if they need to be considering a full fibre contract before it works as expected?

Re: ONT LAN light appears only briefly after power cycle of ONT

KeithFrench — Sat, 02 May 2026 13:51:18 GMT

Hi @fr8ys

Obviously, TT will not be interested in doing anything until after it has gone live. I was merely referring to what the light should do under working conditions.

Re: ONT LAN light appears only briefly after power cycle of ONT

scott_doyland — Sat, 02 May 2026 21:46:31 GMT

I unplugged the fibre cable and then the LAN light comes on.

It seems this indicates an EMS CP TAG error.

Other customers that have had this report days of waiting for it to be fixed, so now I am in a dilemma, do I upgrade to full fibre and hope that by doing so the "error" is immediately fixed by whatever configuration takes place to move me to to fibre, or do I stay with copper.

What I don't want is to move to fibre and wait for days without internet while the "error" is fixed.

Re: ONT LAN light appears only briefly after power cycle of ONT

fr8ys — Sat, 02 May 2026 21:53:04 GMT

You will have to move to fibre at some stage.

We cannot advise you, other than to reiterate that there is no staff presence here so you will need to contact TalkTalk direct.

My own gut feeling is that the ONT box will not work correctly because you are not connected, but really only TalkTalk can advise you.

Re: ONT LAN light appears only briefly after power cycle of ONT

ferguson — Sun, 03 May 2026 13:25:26 GMT

@scott_doyland

Surely it is a simple fact that the ONT will not work if you are not connected to a Full Fibre service?

Re: ONT LAN light appears only briefly after power cycle of ONT

ferguson — Sun, 03 May 2026 15:22:44 GMT

@scott_doyland

And just to go back to your initial question about the ONT possibly being faulty, I think the fact that it lights up briefly when an external device is connected via ethernet suggests otherwise. In any event, if you chose to upgarde to Full Fibre with TalkTalk and that turned out to be the case then a new one would be installed as part of the process.