I recently tried moving my modem from the ground level to the second floor, where I just put in a PC in my office. I have 3 phone jacks upstairs (2 in the guest room and 1 in my bedroom), but it would be much more convenient to run an ethernet cable to the PC if the modem were in the guest room.

Unfortunately, neither of the phone jacks in the guest room work. One blinks green on the DSL light, but the internet light never comes on. The other jack gives the DSL light a solid red.

For whatever reason, the phone jack in my room works just fine (DSL light turns solid green, internet light comes on). I've done some preliminary Googling but haven't been able to come up with a solution, even though I've seen similar posts. I have no phone filters (no landline to hook up), and no splitters.

Any insight would be much appreciated!

  • What's the make and model of the modem? Are there multiple phone lines in the house? Is it possible that the line running upstairs is disconnected? Have you located where the cables are spliced? Have you consulted the manufacturer's documentation to determine what the lights mean?
    – Tester101
    Feb 23, 2016 at 16:51
  • The modem is a ZyXEL C1100Z (issued by my provider, CenturyLink). I've consulted the documentation - the blinking light I'm getting means it's "searching for CenturyLink's equipment," and the red means that "no equipment was found." There are multiple phone jacks, but I have no physical lines connected. I don't believe that the line running upstairs is disconnected, and I haven't located where the cables are spliced.
    – cccg03
    Feb 23, 2016 at 17:19
  • "There are multiple phone jacks, but I have no physical lines connected." Does that mean you don't have phone service, or there are no wires connected to the phone jacks?
    – Tester101
    Feb 23, 2016 at 18:44
  • I have no active phone service. My wife and I just use our cell phones :)
    – cccg03
    Feb 23, 2016 at 19:49

2 Answers 2


Have you tested that the problematic jacks are actually wired to your house's phone system? Just take a land phone and plug it in - do you get dial tone?

If you're not getting a dial tone, these jacks are disconnected. Perhaps they were wired to a second line that is no longer active, or simply cut during some other project. To fix that, you'd need to reattach them, tracing the cables and re-connecting them to your main phone service lines.

If the jacks work for phone but not DSL, there may be a DSL filter installed between your main phone line and those jacks. These can be wired inline somewhere, or even built into the phone jacks themselves. Check the jacks first - do they have DSL-related labels? Can you remove the cover and look inside to see if a filter is there? Perhaps they are connected to another jack that has a DSL filter.

If the filter is wired in elsewhere, you would need to trace the wires from jack to your main phone service termination point to confirm.

EDIT: if you don't have active phone service, you probably won't be able to test with the phone/dial tone method. Instead, you can try a tone & probe kit or test voltage on the lines to see if they're connected to your house phone system. Although I'd still try a land-phone test as it's entirely possible you are supplied with a dial tone even if you can't make or receive calls.

  • Dial tone is usually there for 911, and you can make that call. Of course, they may not own a land-line phone.
    – Ecnerwal
    Feb 24, 2016 at 0:43
  • Oftentimes people who only want DSL also get a bare-minimum phone service, either because it's a prerequisite for the DSL, bundled, or it's cheap. And then they will never use it, and forget they have it. That will typically let you make local, 800 or incoming calls for free. It costs nothing for the phone company to provision this service and they may profit on a-la-carte-priced services like metered long distance, 411, *69, 900#, etc. Feb 24, 2016 at 1:47

I would start by just inspecting each phone jack for any suspicious wiring, note which color goes to which terminal pin on the jack. Back in the "good old days" when a home had a second phone line put in, it was usually wired so that one or more jacks simply jumped on the unused pair of the basic wiring. If you look in the jack wiring and note colors are mismatched where two runs come together, or one jack looks like the colors are arranged differently than all the rest (possibly one of the jacks in your guest room) you have your culprit.

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