Hub 3 modem only mode

[EwanHaig]

Am trying to force my hub 3.0 into modem-only mode. Every time I do it, the front light just turns red (no internet). If I revert to router mode then it is ok. Reading other posts the light should go purple. I have disconnected all wired connections from the LAN ports so there are no external factors. Have rebooted, waited 10 mins etc. No joy.

Any ideas? I need to do this as want to use a 3rd party router as part of a new Mesh Wifi.

Thanks

[carl_pearce]

The HUB 3 LED should be magenta to indicate modem mode, however it can look red.

Don't forgot you cannot have any other wired devices connected to the HUB when in modem mode, just the new third party router/mesh system.

Reboot the HUB once it's connected only to the router//mesh system.

[EwanHaig]

It is definitely red, with no hint of magenta. I also connected just the mesh (TP-link Deco) and no joy (and rebooted). 

[Adduxi]

How are you setting it into modem mode? Once in modem mode connect a laptop via cable set for DHCP and check it is getting a WAN IP. 
If this works switch the Hub off. Setup the Mesh in DHCP and connect it by cable. Only then switch on the Hub. The Mesh should have internet access after approx 10 minutes or so.