I added a Honeywell CM907 thermostat to my system last week. It is a 7 day programmable thermostat. My missus is soon going on mat leave for 12 months so I thought it would be a good time to add one.
I am not an electrician or plumber but managed to instal it very easily. The instructions were ok to follow but what I found very helpful was a video on u-tube. If you search for wireless thermostat boiler instillation it’s by ‘The Ultimate Handyman’ and lasts 15 mins 20 secs. It’s a different boiler to mine but helped anyway. There is also a Honeywell ap that you can download to phones (iOS & Android) and there is a very helpful wiring table.
I have noticed a huge difference in the house, no peaks & troughs in temp.