Just Moved Into a New House?
If you haven't used your washer and dryer connections for a while, were out of town for an extended period of time, installed a new washing machine, or just moved into a new home where the washer was unhooked or the water was turned off for a while, then it's highly likely that the bonnet is leaking. In fact, in most cases, the bonnet will leak after a period of non-use.
How to Repair Your Leaking Washing Machine Faucet
Repairing your leaking washing machine faucet is easier than you think. In most cases, all you need to do is tighten the nut around the bonnet with a wrench, as shown in this photo:
This is as simple as it gets. If you hire a plumber to do this they will roll in with a wrench and charge you $75 or so for the trip over.
Make sure you tighten the nut to a snug fit, but be careful not to over-tighten it. There is packing inside the bonnet that will compress as you tighten the nut (which you'll notice as it may be slightly more difficult to turn the knob after tightening). This packing, incidentally, is was dries and loosens up during non-use, and is usually the cause of the leak. If you over-tighten, you may end up needing to repack the bonnet. If for some reason tightening it does not work, you may need to replace the shut valve. Do not use teflon tape on the bonnet - that will only cause it to leak more.
Once you've tightened the nut, hook up the water lines from your washing machine and turn on the water to see if the leak is resolved. In most cases, this will do the trick. If not, you may need to replace the valve:
Replacing a Leaking Washing Machine Faucet
If tightening the bonnet nut didn't work, you may need to to add new packing material. First, shut off the water to the house. Next, remove the faucet handle, stem nut, and packing nut. Then, remove the stem, discard the old packing material and clean the stem. You'll probably want to clean the inside of the faucet as well while you're in there. Finally, wrap the new packing material around the stem and re-assemble the faucet.