I have a heating thermostat that has optional ‘smart’ features that allow you to control it via your phone. I tried it when I first got it, but it seemed a bit

I have a heating thermostat that has optional ‘smart’ features that allow you to control it via your phone. I tried it when I first got it, but it seemed a bit pointless, so I turned off the feature and the wifi connection. That was a month ago, and the onboard clock has now drifted by around 15 minutes...