Instead of attacking a radio controlled relay, the author should have read up on how their heating system works. All they need is a relay controlled by an internet connected thing to replace the thermostat receiver. I could understand if the receiver was locked away but the video clearly shows they have access to the boiler.
That leaves very visible evidence that things have been hacked. Any time the landlord comes around you'd want to remove that. And if there's some sort of infrastructure emergency (plumbing problem, heat goes out, fire in the building) it could be very challenging to get there and remove all traces before the landlord is stomping around.
People generally don't like you messing with their stuff. They especially don't like it when you add sketchy-looking electronics to things that are expensive and can burn their property down.
If you want to take a swing at it, I'm not stopping you. But after 30 years having landlords, plus having family and friends who are landlords, I think I have a pretty good sense of what can upset a landlord. Maybe yours will be super chill. Me, I'd rather go the radio route.
