When our current boiler was installed we were amazed at how quiet it was.
My associate and I were used to hearing the drone of the old on each time it kicked on plus now we hear nothing.
It is a great feature however sometimes I wonder if it is one or not. There is one funny indicator that I adore telling people about. My Cat! Animals have a much more sensitive hearing ability plus she can still hear the boiler kick on. She instantly runs to the floor vent to wait for the rush of air to come out. She almost seems impatient as she waits. There is always a delay between when the boiler turns on plus when the air comes out. This is due to the high-limit switch. In straight-forward terms this is part of the boiler plus makes sure the air is heated before sending it through the air duct. If your system did not have this it would blow cold air until it was able to heat it up each time. This would be like blasting the heat in the vehicle while the engine is still cold. You would be irritated during that time plus it would make you colder than you were plus it would take longer to heat the space or your car. If you ever notice that your boiler is blowing undoubtedly cold air prior to moderate air you may want to have this part evaluated to make sure it is still laboring regularly. Because this part gets a lot of use it can wear out over time plus should be part of your official tune up routine too.