Bleeding a Boiler

[Mike]

What is the proper way to bleed a hot water boiler w/radiators? Is it normal for the system to use water if there are no leaks?

[Mike Grooms]

"Mike"

Water has dissolved air in it that bubbles out and gets trapped in radiators, not allowing the hot water to flow fully. Each radiator should have a little bleeder at the top that operates with a little wrench or screwdriver. These bleeders might also be at high points of the piping where the pipe goes up and then down. Repeated bleeding is needed till all the air is eliminated. Since a boiler uses the same water over and over, eventually, all the free air gets eliminated.

If your system is typical, then, no it shouldn't use much fresh water. Maybe the relief valve is leaking, or blowing off for some reason, but when fresh water is introduced into the system, with it comes more dissolved air. Then the bleeding must take place again and again.

Again, if your system is typical, the pressure gauge should read about 14 psi. If it's much greater, then the automatic fill valve is faulty. The temperature is a harder call, since systems vary so much, but if it's more than 200 degrees, there's probably a problem. You might also simply have a leak in the piping that's undetected.

[Mike]

I continue to have to bleed the system. I do realize introducing new water brings air, so I must install some auto bleeders. Where do you recommend them going? I get a bang after the circulator pump turns on after approx. 10 seconds. The bang seems to be coming from the closest radiator to the boiler. Today I noticed the system pressure dropped to 11 psi.. The climate is a little milder lately and the boiler has run less. I don't know if I am only watching it more because of the bang or if the psi has done this in the past. But I always thought it stayed at 14 psi. Temp set at

180*F. I also thought the accu-stat may have been at fault so I turned it up to test for the heck and when set at 220*F it boils near 212*F which would be correct. How do you determine how full the steel non-bladder tank is filled? Thank You, Mike

[Mike Grooms]

"Mike"

If your expansion tank is waterlogged, the pressure relief valve will run every time the boiler kicks in. Can you see where the relief valve drains?

The automatic bleeders are usually placed near the boiler, on a high area of the main feed line.

[Mike]

The relief valve drains to the side of the boiler to a drain (dry, no relief opening) Automatic Bleeder: main feed to radiators or the auto fill line? Tx, mike

[Mike Grooms]

"Mike"

The feed to the radiators, or on the high pipe that goes to the expansion tank.

[Mark Monson]

If you have the non bladder type of expansion tank, you should not be using automatic bleeders. If you have problems with air in the radiators it is likely from low pressure, not using a boiler fitting on the boiler, not using an ATF on the tank, or not properly piping the tank to the boiler. You have to continuously separate and return air to the expansion tank or you will get air bound in the radiators and water logged in the expansion tank.

MM

[Mike]

You have to continuously separate and return air to the expansion tank or you will get air bound in the radiators and water logged in the expansion tank.

How do you accomplish this separation?

[Mark Monson]

Call a plumber or hydronic heating tech. You want something to putter around with, get a model train kit. A boiler can be a bomb - not something for the unqualified to goof around with.

MM