The obvious question is any error code on the screen at all? W5 is a chip failure, but as you can reset the thermostat wifi, you obviously are not seeing that error!
The other question are you in the UK, and how old is the stat?
There are many reasons for loosing wifi connection, but the most common are objects, and connection to a wifi booster/mesh acess point. Yes the thermostat might have worked for a year, but have you connected direct to the router? Have you placed any new objects in the house, ie: Microwave, fridge etc., etc? These all block the signal especially from a booster.
Resetting your router or display most of the time does't fix the issue in my experience, but always worth a try. I would check for any new item inside the house first of all.
