The thermostat has a schedule which can be set in the app or on the unit itself too. Instead of a typical on/off like a rotary timer might have on the boiler itself, the thermostat will have a timer based on temperature. So in an 'off' period, it may still turn on to turn the temperature to 15C. This will result in the house never getting too cold, but not unnecessarily turning the boiler on at the same time to target a warm temperature.
An example would be to have the temperature targeting 23C in the morning between 7AM and 9AM, then setting back to 14C between 9AM and 6PM, then 22C from 6PM to 10PM.
The thermostat will show a flame icon when the target temperature is above the current temperature and has sent a 'Heat On' command. However, if the boiler switch was manually switched, then the thermostat will not reflect this. It is also possible the boiler switch was out of range/did not receive this command, though you would see a flashing radio/antenna beacon at this time if this is the case.
The Thermostat unit will link to your central heating (not hot water) by our Boiler Switch. The Boiler switch links to the Thermostat, the Thermostat can link to the WiFiLink/app too, if desired.