View Full Version : Boiler bleeding
frank in ohio
10-02-2009, 10:15 AM
I have a Weil Mcclain oil fired boiler that I am trying to bleed, having some success, but not quite right as I can hear the water flowing when the circulator turns on. Also, it seems to build up to the cut off temperature more quickly than before, thereby shutting down the burner. There are 2 zones and each baseboard radiator has a bleeder valve. All that is on the boiler itself is a drain valve at the very bottom. There is no "quick fill" valve or any other locations to attach a garden hose as I have seen mentioned elsewhere on the web. Anyway, what I am doing, one zone at a time, is waiting for the boiler to get up to some temperature, then opening each bleeder valve one at a time, first closest to the boiler, then next, and so forth. I don't seem to be getting any air, but can still hear the water flowing so I don't think I'm doing it right.
Any suggestions would be appreciated.
10-02-2009, 03:25 PM
To get air out, you need more water in...do you have an auto-fill valve or do you need to open a valve to get water in the system? What's the operating pressure? What's the manufactuer recommend (probably around 12-16# or so). If the pressure is too low, it can flash boil, and shut itself down.
frank in ohio
10-02-2009, 03:52 PM
I think it's autofill. The water line goes into this "thing" which the water line connects to on the side, the bottom of this "thing" has the pressure tank connected to it, the top side goes to another device that says "automatic air purger" on the side of it. This "automatic air purger" is in line with the boiler output to the zones. On top of the "automatic air purger" is a device that has an air valve on top of it. I checked the air pressure at the bottom of the pressure tank and there wasn't much, if any. I added some air, got it up to about 15 psi, this seemed to have helped things meaning that the temperature does not go up nearly as quickly as before. Maybe that's all I needed.
10-02-2009, 08:53 PM
Between the potable water and the boiler loop, you need a backflow preventer and you may have an autofill valve. If you have an autofill valve, the pressure should have automatically been maintained at the setting of the valve (which should have been set when installed). If it was quite low, and you raised it by adding air to the expansion tank, you either don't have an auto-fill valve, or it isn't working, or the supply valve to it is shut. If all you have is the backflow preventer, then you'd need to open the supply valve to let some water in while watching the pressure gauge to get the proper fill pressure.
To best set the air pressure in the expansion tank, it should be done when there's no pressure on the water side. Most boilers have a pressure gauge, or an electronic readout, and your manual should tell you what it should be. If your expansion tank is shot, the pressure will go up while the boiler is heating, and drop again when things cool off. If it is working properly, the pressure will stay nearly constant. If the system pressure is too low, things will boil, just like in your car if the pressure cap leaks or the level gets low.