One ADSL line 2 Modem/Routers?

When I have had connection issues one of the inevitable questions that my ISP asks is "If you use a different modem/router does the problem go away?"

Well, I now have a spare modem/router and am consequently wondering if there are any technical reasons why I can't put them both on my ADSL line using a suitable splitter on my modem cable (RJ11 in, 2x RJ11 out).

Presumably
- the splitter will cause a certain amount of interference on the line
- I have to ensure each router uses a different SSID and WiFi channel

If I lose connection, I can then from my PC quickly see if I can connect through the "other" router/modem and thus rule modem/router problems in or out?

You can only have one ADSL device at a time as it is a communication technology that only works between two devices, the DSLAM at the exchange and the modem/router at your home. So the best solution is to have the spare device configured and tested and then plug it in when you need it. You probably won't have to do this very often. (IME!)

Thanks I rather expected that to be the case.

Having said that, having acquired the spare router my existing one has behaved perfectly!

On the other hand, BT have repaired the manhole (one of those with concrete manhole covers - which can't take the weight of a lorry that chooses to park on the pavement!)