He also now said that he's not familiar with the type of smart home system I brought so not sure what will happen when we come to fit
The reality is that there are so many different controls and smart systems.
You call him a "plumber" but seem to expect him to be an electronics and computer expert as well.
Most plumbers can fit basic controls like timeclocks and stats. But advance that to the Evohome system and it really helps to have been on their course. But that is only one of so many control systems.
There are still many plumbers who are totally unable to wire up anything at all, not even a mains supply into a boiler. They need to call an electrician. That sounds an easy option but many electricians are out of their depth with heating controls.