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.

  • 3
    STOP! That "barrel in the ceiling" is likely an expansion tank, which is mostly filled with air. If you release the air, it will fill with water and no longer function. Unfortunately, the pinging and popping is likely the plumbing of the heating system expanding. These are normal sounds caused by the expanding metal rubbing, grinding, and straining against itself and other materials.
    – Tester101
    Commented Jan 22, 2013 at 15:47

2 Answers 2


Bleeding radiators is quite simple, and can usually be done by homeowners. All that's required is a radiator key, a towel and/or bowl, and a bit of time.

Why Bleed Radiators

Even with closed systems, air can still find its way into the system. When it does, it will collect at the highest points available (the top of radiators). Trapped air can cause radiators to heat less effectively, so removing it will help reduce your heating costs.

How to Bleed Radiators

To bleed the radiator, you'll need a special tool called a "radiator key". A radiator key is a small key like object that will fit on the bleed valve of the radiators, and is used to open/closed the valve.

enter image description here

The first step in bleeding the radiators, is to turn off the system. Next, you'll have to locate the bleed valve on each radiator. This valve should be near the top of the radiator, and will look something like this.

enter image description here

Insert the key into the valve, and hold the towel and/or bowl below the valve. Slowly turn the key anticlockwise, until you hear a hissing noise or water starts to drip from the valve. Once water starts to drip, close the valve by turning the key clockwise.

enter image description here

WARNING: Never open the bleed valve too fast, too far, or completely remove the valve stem.
CAUTION: Water dripping from bleed valve may be hot. Contact with aforementioned water could lead to injury.

Repeat this procedure for each radiator in the system.

Repressurize the System

After bleeding the radiators (or even before bleeding the radiators), you may notice the pressure in the system is too low. The typical rule of thumb is that for a 2 story home, the pressure should be between 12-15 lbs. or 25 - 30 ft. If you notice the pressure is a bit low, you'll want to top the system off.

There should be a supply pipe connected to the boiler, with a valve that is fully closed. This pipe should come from the cold water supply system of the house. Once you've located the supply and valve. Open the valve slowly, keeping an eye on the gauges, close the valve again when the gauge reaches the optimal level.

  • 1
    Thanks a ton. I don't have one of those keys, but I will search the 'net and my local hardware stores for one that works with mine. Are these keys (relatively) standard?
    – JZeolla
    Commented Jan 22, 2013 at 17:28
  • 2
    Honestly, I don't know that much about the keys. Take a look at the valve, it might allow you to turn it using a screwdriver.
    – Tester101
    Commented Jan 22, 2013 at 17:36
  • 1
    Pretty good chance your hardware store will have them.
    – TomG
    Commented Jan 23, 2013 at 3:02
  • I have two gauges. One shows 0 psi but has accurate temperature. I'm not sure what the other is. Thoughts? i.imgur.com/VjWHMf3.jpg i.imgur.com/RGpFcwh.jpg
    – JZeolla
    Commented Feb 4, 2013 at 11:41
  • It's hard to see the gauges, they are washed out due to the flash.
    – Tester101
    Commented Feb 4, 2013 at 11:57

If your hot water heating system is making noise it's likely because there's air in the pipes. Why it happens at 5am regardless of what time you set the thermostat is odd but maybe it's related to what time you set your alarm clock?

I don't think bleeding the system will necessarily get rid of the noise if the noise is coming from the pipes. In my experience what bleeding helps with most is making sure there is no air in the radiators. If you touch the radiator towards the top and it's much cooler than it is near the bottom when the system has been running then your radiators need to be bled.

The cylinder you mentioned sounds like your expansion tank. The cylinder shape sounds like it's an older style expansion tank without a diaphram. These need to be emptied once a year. There should be a valve before the tank that allows you to shut off the flow of water to the tank so you can drain it. Draing it can be slow if there's no vent to let air in or it's mounted in a way that makes it impossible to open. Just have to wait while it glugs glugs glugs its way empty. When you're draining it make sure the system is off and cooled first. Best to do before you turn on the boiler. Don't forget to open up the valve to allow water to enter the tank again.

You may be able to go a couple of years or so without draining it but it's best to just get in the habbit of draining it every year.

Boilers usually have internal ways of eliminating air from the system. Some may have an automatic air vent. It's a small metal component that's one of the components that gets rid of air. These can go bad and need to be replaced. Easy to do. Just unscrew the old, screw on the new. Don't remember if you need to drain the system first or not. Last time I replaced mine I had to drain it to replace the pressure releif valve. May look something like this.

enter image description here

One more thing that need service (but not related to making noise) you probably have a circulat pump in your system. These need to oiled once a year. The manufacturer of mine makes their own oil but everyone tells me to use Mobile 1 SAE 5W-30, even the manufacturer when I called them.

Lots of things can go wrong with a heating system, some in a very catastrophic way. At the very least you should find and read the manuals for all your components (should be hung near the boiler or can find online). Typical systems will have the boiler, pump, expansion tank, pressure reducing valve, pressure relief valve that need periodic attention. Every few years a thermocouple or relay might go bad and need to be replaced.

You might want to also hire a reputable heating contractor to come to inspect your system and give you a lesson in how to maintain it. Maybe even identify any leaks that allow air to come into the system.

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