I'd like to preface this post with the fact that I'm a complete diy amateur. I may say stupid things, or things that make no sense. Please feel free to correct me as I'm always open to learn.
So, it's winter in my area and it seems like pretty much every morning at 5am, I have some pretty loud sounds in my house. They're pretty much like pinging and popping sounds.
I suspect that it's my furnace, since I've never heard these sounds in the summer (I turn the boiler off in the summer, pilot light and all), and I did experience this last winter but to a smaller degree. At that point I suspected that it was just the house settling.
I have a central boiler with connected rads in each room. What is strange though, is that I've changed the time when my house heats up (I've heated up the house at 4:00am, and at 6:00am) and I still get the sounds at 5:00. Is it possible that there's some sort of a self-test going on? I really don't know much about boilers.
From what I've read, a lot of people suggest bleeding the system, but I'm not 100% sure how to do that. There's a sort of barrel in the ceiling of the room where my boiler is, with a typical valve and threading where I could hook up a hose. I want to say that this is the expansion tank, but I'm not sure.
I'm not sure if I should just attach a hose there and open that up until water flows steadily or what? Since my boiler is a "closed system" and just uses this tank when overflowing (by magic?) I'm guessing that I should not do this. How can I be assured that my boiler will self-fill itself if I overdrain?
Other suggestions have said that I should go to the highest point in my house and open up the rads individually until water flows (while the water inside is hot? cold?), then shut it off, and systematically hit each radiator moving down the floors until I've done them all. Although I've never been able to find a legitimate article that says whether this applies only to standalone radiators, or also to closed-circuit boiler systems. I did take a quick look at one of my rads and found something that seemed like it may be used to bleed the system, but it looks like if water came out of it that it would be very messy and hard to control.
If anybody could provide me with some reading materials about how these systems typically work as far as how they self-fill and self-regulate, etc. (I have done some Googling and reading, but didn't find a single good resource) that would help a lot as well.