Ethernet Works, Coax Doesn’t: What to Check

A combined Ethernet and coax wall plate looks like one outlet, but its two connections lead through different cables and equipment. The RJ45 port may run back to a patch panel or network switch. The F-type coax connector may lead to a splitter, cable provider feed, antenna system, or MoCA network. If one side stops working, replacing the entire plate immediately may leave the real problem untouched.

This guide helps you narrow down the fault before buying parts or opening the wall. It uses the R.J. Enterprises RJ-EC-04 bundle—a two-port plate with a blue Cat6 RJ45 keystone jack and an F-type coax connector—as an example. The same troubleshooting approach applies to many combined Ethernet + coax wall plate bundles.

First, identify which service has failed  

Start by writing down exactly what works. Does a computer plugged into the RJ45 port get a network connection? Does a cable modem, TV device, or MoCA adapter connected to the coax port receive the service you expect? Has either device worked at this outlet before?  

That last question matters. An unused coax wall connection is not necessarily connected to an active provider feed or to the other coax outlets in the building. Likewise, an Ethernet jack can be correctly installed but not patched to a switch at the other end. A wall plate provides connection points; it does not activate a service or connect two separate networks by itself. 

Check one side at a time. Use a known-good device and a known-good short cable where possible. Record what changes when you swap them. These small tests often tell you more than removing the plate and looking at the wiring. 

When Ethernet works but coax does not

If the RJ45 port works, you have useful evidence: the Ethernet side of the outlet is functioning for the device and connection you tested. It does not prove that the coax cable, F-type connector, splitter, or service-provider feed is working. 

Begin with the accessible coax connections. Check that the cable is properly seated at the wall and at the modem, TV equipment, or MoCA adapter. Look for a damaged cable, a bent center conductor, or a connector that will not thread on cleanly. Follow the equipment maker’s instructions; do not force or overtighten a fitting. Xfinity’s connection guidance notes that loose cable connections can cause service problems.  

Next, determine what the coax run is supposed to carry. If a cable modem will not connect, check the provider’s outage and equipment diagnostics before blaming the plate. If the problem appeared after equipment was moved, confirm that the new outlet is actually connected to the intended feed. A splitter may also be part of the path. Xfinity’s splitter explanation shows how one coax feed can be divided among devices; finding a splitter is not, by itself, proof that it is connected correctly for your service.

For a MoCA setup, trace the path between adapters rather than assuming every coax outlet is linked. Splitters and other equipment in that path must suit the installation. Our MoCA wall plate guide explains what the wall plate does—and what still depends on MoCA equipment and the coax network.

A technician can test a disconnected coax run for an open, short, or distance to a fault using suitable equipment. Fluke Networks’ coax testing guide illustrates those results. Follow the tester’s instructions and do not connect a continuity tester to active service or powered equipment. If the run tests correctly but the device still has no service, the fault may be elsewhere in the signal path.  

When coax works but Ethernet does not  

A working coax service does not tell you whether the RJ45 jack is connected to a switch, whether its cable is correctly terminated, or whether the device’s patch cord is good. Start outside the wall: try another Ethernet patch cord, a known-good device, and—if you control the network—the correct switch port. Check the link indicators on the device and switch. 

If the outlet leads to a rack, identify its matching patch panel port. Confirm that the panel port is patched to the intended switch port and that the switch port is enabled. This is where clear documentation pays off: the room outlet, permanent cable, panel port, and current switch assignment should be identifiable. Our guide to labeling a drop from wall plate to patch panel shows how to keep those records separate.

Once the easy swaps and rack-side checks are ruled out, test the permanent Ethernet run with an appropriate cable tester and a remote at the far end. A wire-map test can reveal opens, shorts, reversed or crossed pairs, and some split-pair faults. Fluke Networks explains typical wire-map faults. Keep in mind that a basic continuity or wire-map pass does not certify the cable’s category or prove that it will support every desired network speed; Fluke’s wire-map overview makes that distinction.

If testing points to the room end, inspect the keystone termination and follow the jack maker’s instructions for repair or replacement. If the cable already has an RJ45 plug and the installation calls for a pass-through connection, a coupler is a different component—not an interchangeable name for a keystone jack. Our keystone-versus-coupler guide explains that choice. 

What if neither side works?

Do not assume there is one shared fault merely because both ports sit in the same plate. The Ethernet and coax services may have unrelated problems. For example, a network switch could be disconnected while the coax feed to that room was never activated.  

Check the service status and equipment for each path independently. Then inspect the visible outlet for physical damage: a cracked plate, loose insert, pinched cable, or signs that the assembly was disturbed during a remodel. If the problem began immediately after work in the room, that timing is worth telling the installer or technician. It is a clue, not a diagnosis. 

Repair the failed part, not the whole network 

The best next step depends on what the tests show. A bad patch cord calls for a new patch cord. A loose coax connection may need to be properly reseated. A failed keystone termination may need to be reterminated or the jack replaced. A damaged in-wall cable, unsuitable splitter, inactive provider feed, or disabled switch port requires a different fix.

Replace the wall plate or connector when you have evidence that it is damaged, cannot hold its insert securely, or no longer suits the connection you need. A bundle such as RJ-EC-04 can provide a clean Cat6 RJ45 and F-type coax endpoint for an appropriate replacement project. It cannot repair a break farther down either cable or substitute for the equipment that supplies Ethernet or coax service.

If replacing the outlet is the right call, plan the physical work carefully. Our finished-room installation guide covers mounting, cable handling, and testing. For unfamiliar in-wall routes, provider-owned connections, or work near electrical wiring, use a qualified professional.

A combined wall plate is easiest to troubleshoot when you treat its two ports as two paths. Test the devices and short cables first, trace each path to its source, and replace only what the evidence identifies. That leaves you with a working outlet—and a much clearer record for the next time someone needs to service it.