Problem with Hive

When British Gas fitted my new combi-boiler three and a half years ago, they also installed Hive.
I was very nervous about this, but one of my daughters loves this system as it can be totally controlled from a smartphone. So, have learned to use it and 'Yes', it is convenient.

My flat is quite warm, so only last evening I thought I should be thinking about having it back on - and tried to do a one our boost.
No radiator came on. Neither did the boiler, neither did the wall mounted Hive controller.
Panic on my part - not that I was particularly cold but what to do. Phoned daughter who lives nearby and bless her - she came straight round.
Fiddled with my phone - to no avail. I got more and more upset - then she went into Hive Assistance on her phone.
All that was wrong was that the wall mounted Hive Controller required the batteries to be replaced. Neither of us (and she uses Hive also), had any idea that this little gadget used batteries.
Four double A's changed and straight away everything worked as it should. I was most grateful. If she had not come over and sorted this out I would be telephoning BG for an engineer to come today.
Technology can be so wonderful - and so very difficult for my 85-year old brain to cope with when it does not work.