Is the modem physically located next to the TV, so you could run a network/Ethernet cable directly from the modem to TV?
Also, do you have other devices working on your home wifi already?
not possible to run a cable Our other TV and computer upstairs/iPads all running perfectly
The Hisense TV can't see to find the router? It's close by with a thin plasterboard wall between, would a range extender help at all?
The standard or normal Wi-Fi range of a basic modem is up to 10meters.
Were you able to check if the TV is not detecting your TPG router only or no Wi-Fi connections is being detected at all? If your TV has a built-in Wi-Fi cast, then it should at least be able to detect your Wi-Fi or any other Wi-Fi networks available, unless it is really out of range.
An extender may also help however, I would highly recommend to seek help first from a professional at an electronic store and show your current network set up so they can advise which Wi-Fi extender/booster would work best with your devices.
My other devices are connecting ok to the TPG router, just not the Hisense TV, yet this TV worked perfectly with our Telstra router
The Hisense manual says the TV will connect 'more easily' if the router supports DHCP, and 'if you have a security system it must be WPA. WEP WPA2
This is all meaningless to me I'm afraid
Will a better non TPG router conected to the NBN box do the trick
If you take your ipad next to the Hisense, you can check the relative wifi signal strengths (number of bars) of both wifi bands from your router. And also the neighbouring networks.
On your ipad, look at settings/connections to see the ipad's own connection, tap it and it should show what security is being used, most likely WPA2.
Normal mode for router is DHCP mode.
What model Hisense is it?
Have you tried a factory reset on it? It might have some remembered info from Telstra router.
If you are worried about signal strength, in the first instance, can you move it next to the router? An extender won't help if there is something wrong with Hisense or the setting up is wrong.