Ethernet connection working from router but not from mesh LAN port

[Fluss]

Hi all,
I have been troubleshooting an issue, but I can't work out what's going on.
Firstly, I'll explain setup.
I have an ISP supplied router which I am augmenting with wi fi mesh units (Tenda nova MW6 - 3 pack)

During to a recent loft conversion, I had the foresight to get the electrician to install cat6 cable from the ground floor, where the ISP supplied modem/router is, to the new loft room, for latter installation of a Mesh node/AP. The cat6 cable is terminated with wall sockets at both ends. Prior to setting up the mesh system, I connected the existing modem/router - via one of the four lan sockets on back of router - to the upstairs socket, then to a laptop via an ethernet patch cable - to ensure it was working before I signed off the job. I could connect to the internet via the LAN without problem.
Wind the clock forward to where I am installing mesh wi fi: I am unable to get ethernet back haul working on the loft mesh node. It keep connecting via wireless back haul only.
I am able to connect the loft node to the master node with a short ethernet patch cable, and the config app shows the connection as wired back haul, but as explained, if I substitute that for the lan connection to the loft it doesn't work! Since I know the lan connection from the ground floor to the loft is working, I can only think that the mesh lan port doesn't put out enough power to reach the loft via a longer cat6 cable? However, I added an unmanaged powered switch between mesh node 1 and the ethernet wall socket that runs to the loft room, but no difference.
I have tried swapping the mesh units round, but no difference. I inspected the wiring in the wall sockets, to check they were wired correctly, or in case the main modem/router is able to handle incorrectly wired wall sockets/crossovers, but the mesh node cannot. I can confirm that the wall sockets are wired as T568A as expected in a UK residential setting - on both ends I might add

Can anyone suggest anything to help.. this makes no sense why router can supply connection to loft, but via mesh LAN socket, it cannot, even though mesh LAN socket has been proven to provide a connection, when not using LAN connection to loft, but a shorter patch cable.
BTW, all my patch cable are T568B pinned, but that should not make a difference as they are wired the same at both ends of the patch cable. (straight though)

I should add that I have tried mesh wired back haul both in router and in bridge/AP mode and neither works with respect to the above topology.

 

[coxhaus]

You are throwing out there T568A and T568B terms. You can end up with a crossover cable if not careful. A gig port will work with a crossover cable but a fastEthernet 10/100 port will not. The other thing is remember 2 crossover cables make a straight cable.

 

[Fluss]

You are throwing out there T568A and T568B terms. You can end up with a crossover cable if not careful. A gig port will work with a crossover cable but a fastEthernet 10/100 port will not. The other thing is remember 2 crossover cables make a straight cable.

Thanks for your reply. I only mention the configuration of T568A from wall socket to wall socket, to confirm that the LAN has been wired correctly and that it has been tested - to eliminate replies suggesting I should check the wiring. Besides, as mentioned I get a connection when connecting: Modem/router --> LAN --> laptop. But the mesh node in loft won't seem to use the LAN as wired back haul. Besides the primary mesh node (gateway) in fact all nodes, does have a gig port for wired back haul.
Either way I am very confident that there are no crossover connections in my set up. I have checked wall sockets and all patch cables.

 

[Fluss]

So... I did another test by using a 20 meter lan cable in place of the LAN connection to the loft, from the primary node to one of the other nodes. This LAN cable is actually longer than the one in situ that goes to the loft. Once connected by ethernet, wired back haul was shown to be working! This suggests that either there is some problem with the LAN cabling or sockets to the loft - which would be weird as I can get a connection to the loft if I just take a connection from the router via the loft LAN into a laptop, or for some reason the gig LAN port on the primary node doesn't like the loft LAN!
this makes no sense really, unless perhaps the loft LAN is only "partially" working?!? I'm going to check to see if there are loose or disconnected pairs in the sockets and try again. Grrr..

 

[Wekiwa67]

I'm going to check to see if there are loose or disconnected pairs in the sockets and try again. Grrr..

We had the same issue on our new house! Contractor didn't terminate several jacks correctly. Very irritating to trouble shot a new system after we received a commissioning report. I kept a 15% retainage until they got it right.......

 

[Mark0]

Did your test laptop upstairs connected to the wall jack show the connection is gigabit? Gigabit uses all 8 wires, 10/100 only uses 4.

You could unscrew the wall plates and look at where and how well the wires are punched in, most are color coded to match the wire colors.

 

[Keith Gorham]

Check ebay for a cheap (less than $5 usa) for a cable tester.

 

[Fluss]

Problem solved. Thanks everyone for your useful suggestions.
@Wekiwa67 yup, a real pain and allot of wasted time.
@Mark0 I didn't check to see if I was receiving gigabit via laptop upstairs, but that would have helped as it would also have suggested a partial connection.
@Keith Gorham Yes, I ordered one on Thursday which came today. It confirmed that pin 3 (orange and white) wasn't connected at one of the ends. My eyesight isn't great, so that was useful when poking around.
Using a magnifying glass, I could clearly see unseated cable with some sheath wedged in the slot! A quick removal and punched down the wire, tested and now have wired backhaul to the loft node.
..happy dayzz.