Your friends are over and, because it has been so cold, you made some nice hot tea for everyone to enjoy. Between the tea and the boiler, you and your guests should be nice and comfortably warm.
Your only problem right now is that you could swear you can still hear the kettle whistling to alert you that the water is hot. You’ve checked the stove is off and the kettle is quiet, so where is that noise coming from?
The source of the sound may actually be from your boiler. And while the tea is nice and warm, if your boiler is making this noise, everyone may not be able to get as warm as you originally thought.