Can I use button to override app/thermostat

My phone is lost and thermostat is not working..I find if I press the unde button once, boiler switches on for 15 seconds and then off. Can I use the button to force override on or off... I thought so. But seemingly only for 15 seconds 😒

My phone is lost and thermostat is not working..I find if I press the unde button once, boiler switches on for 15 seconds and then off. Can I use the button to force override on or off... I thought so. But seemingly only for 15 seconds 😒