Leaking air separator on boiler

Ever since we did the basement water work, I have been very diligent about checking the basement floor after it rains to see if there is any seepage. Imagine my surprise then, this morning when I venture down to the basement (after last night’s downpour) to see this:

What the? Holy Hand Grenades Batman!

Oh no, wait, that is not coming up through the floor, it is dripping on the floor… from the boiler expansion tank… or something right above the boiler expansion tank like the air vent. That seems odd. This unit appears to be leaking right along the top seem. They are relatively inexpensive, so I just went to the local hardware store and picked up a TACO 400 Hy-Vent for about $8.00.

Old leaking air vent.

This is the new air vent with pipe thread compound applied, ready to install.

I did not drain all the water out of the system to replace this, I simply turned off the boiler feed valve. Then unscrewed the old unit and quickly screwed the new unit in its place, using a little pipe thread compound on the air vent thread to make sure it does not leak. I did this when the boiler was cold to avoid being scalded. Some water leaked out while I was doing this, maybe 2-3 ounces or so.

The installation instructions on the box read:

Screw valve vertically into tapping by hand (DO NOT USE WRENCH) making certain that the cap is screwed down thightly, to prevent scale and dirt from rushing in to valve while filling system.

After system is filled, loosen cap slightly and allow air to be released slowly, otherwise scale and dirt might rush in causing valve to leak. If this does happen, push down valve stem then pull up lightly to dislodge scale.

To shut off valve, screw cap down thightly (sic), for normal venting, open cap on full turn, wherever there is a possibility of water damage, use a waste connector and run tubing to nearest drain.

An air separator in a hot water heating system bleeds air out of the pipes so that the system works correctly. It has an air vent on the top of it. The air vent has a little float in it and when there is enough air in the top chamber, the float drops down, opening a small valve and you hear a little “ssssst.” They are important because too much air in a heating system can cause pump cavitation, knocking, excessive corrosion of cast iron parts, and/or complete system failure.