My flat is where wireless signal goes to die. This little booster plugs into a socket in my hallway, halfway between Hub and boiler. The British Gas engineer who installed everything provided it free of charge when he couldn't get the system to work.
The app also has a "geolocation" feature that reminds you if you've gone out and left the heating on. It senses where your phone is in comparison to your home, and can turn your heating on if it's cold and senses you coming back.