The flame on my app/thermostat is displayed indicating the heating is on, however my boiler isn’t on. Is this normal? (WH)

This is perfectly normal and your system is working correctly. The flame symbol shows your room/zone has not yet reached the set point, however your boiler will go on and off according to the algorithm. As the room/zone gets close to the set point, the time the boiler is on will decrease. This basically means the boiler is ensuring that your room doesn’t over heat and you don’t waste energy