It's a modulating boiler, it's not on/off, rather it has levels. The lower the level the more efficient it is. It's better to run the boiler on low for 3 hours

It's a modulating boiler, it's not on/off, rather it has levels. The lower the level the more efficient it is. It's better to run the boiler on low for 3 hours, vs high for 1 hours. How do you know if to run the boiler on low or high? You check the outdoor temperature. You also do a backup: If the boiler has been running for more than an hour, increase the temperature slightly every 15 minutes. Once it goes off, reset the temperature to the one determined by outdoor temperature.