If your wiring centre only works with the last thermostat you paired, then its likely you have adjusted the ID number of the wiring centre after each time you paired a thermostat.
When setting up your wiring centre, you need to setup a unique ID with the rotary switch but you should only do this once.
Ensure you set the unique ID number and then pair each thermostat to it.
More information on pairing neoAir to the UH8-RF is available here
Information on pairing the Slimline-RF to the UH8-RF is available here