@ferncot Yes, as @imjolly has said the SH2 must be the first connected device to the ONT for DV to work.
You then can do one of two things.
1. Keep the SH2 as your main router and add a third party device purely as a wireless access point by turning off the DHCP server in the secondary device, giving it an IP address outside of the range of the hub DHCP server and a Gateway address of 192.168.1.254 Connect the 2 devices LAN port to LAN port.
2. Disable DHCP and wifi on the SH2 and connect your secondary device WAN port to a SH2 LAN port and use the secondary device as your main router. Again give the secondary device an IP address outside of the DHCP range of the hub (although it is turned off) and Gateway 192.168.1.254. You need to make sure the secondary device is a different subnet to the hub's 192.168.1.XXX range. You will be double natting if you do this, but unless you are a serious online games player, that shouldn't be a problem.
Thanks for that licquorice
At the moment I have a dual wifi network, one for me with full access and one for guests which is an internet only network. I know that if I use the SH2 as the first connected device my devices loose that ability. So I was just wondering if I set up as your option two, would it be possible to have the SH2 outputting a separate wifi signal that was isolated from the secondary router's LAN and WiFi network?
With option 2, the WiFi is turned off on the SH2 so you can continue to use your guest network as before on the second device as if the hub wasn't in circuit.
Thanks again licquorice.
when I have tried to connect my router to the SH2 in the past the guest account couldn't be separated, but I may have got the settings wrong. I will give it another try.