How a frost-free sillcock works

A frost-free faucet is only frost-free with the hose off. We would letter that on the siding beside every one of them, because the faucet does its real work inside the wall, where nobody looks, and a garden hose is the one thing that can stop it from working.

Where the water actually stops

A plain hose bibb shuts the water off right at the outside wall, so the water behind its handle spends the winter outdoors. A frost-free sillcock moves the shutoff indoors. Woodford, which makes them, puts it in two lines: the water is shut off several inches into the home, and the water line does not freeze because of the heat in the home. PRIER’s specification sheet for its freezeless wall hydrant says the same in its own words: the valve is connected to the supply piping in the heated portion of the structure.

What you see outside is only the handle and the spout. Behind them a long stem runs through a tube, the barrel, to a rubber washer at the far end, and that washer closes against a seat on the warm side of the wall. Turning the handle turns the whole rod. Because walls differ in thickness, these faucets come in lengths: PRIER stocks its wall hydrant in lengths from close coupled to 24 inches, with longer sizes on request. Legend Valve’s instructions ask for at least 2 inches of the inlet connection to be exposed in the heated space, and warn that the sillcock will resist freezing only when the inlet connection is located and exposed within a heated space. A sillcock that is too short for its wall puts the seat, and the water behind it, back in the cold.

Why the barrel drains

Shutting the valve leaves the barrel between the seat and the spout holding water for a moment. Woodford: when the valve is turned off, all of the water in front of the valve drains from the faucet, leaving the tube empty. Two things make that happen.

The pitch. Woodford’s installation sheet says the tube must have a slight downward pitch for proper drainage, with the nozzle pointing down. Legend Valve gives the only number we found: bore a 1-inch hole through the foundation wall or the floor joist band, pitched upward at a 5 degree angle. Rising toward the house, that tips the barrel down toward the spout. A sillcock set level, or sloping back toward the house, keeps a puddle in the barrel, and the puddle sits in the cold part of the wall.

The open spout. Woodford’s drawing says the faucet must be installed with downward pitch toward the nozzle and the hose must be removed in freezing weather; with the hose removed, it drains on its own. A hose, a splitter or a hose shutoff on the threads holds the barrel full. Structure Tech, a home inspection firm, explains the result: if that water freezes, it can burst the stem of the sillcock.

The tell that comes in April

A split barrel is quiet all winter, because the burst is past the shutoff; Woodford notes that only a few drops leak when the tube bursts. Structure Tech notes that most homeowners do not know it has happened until the first time they use the faucet in the spring. Then, as Structure Tech puts it, once the faucet is turned on, water starts shooting out of the burst stem inside the house. That is why our April page says to turn the outdoor water on and look inside the house below the faucet.

A tell you can use any day of the year comes from the City of Bend, Oregon: after you shut the faucet off, if water drains from the spout for a few seconds, that is a good indication the hose bibb is frost-free. A faucet that goes dry the instant it closes may be a plain hose bibb, or a frost-free one that is not draining.

The vacuum breaker on top

Many frost-free sillcocks carry a cap on top of the outside body: the vacuum breaker. Its job has nothing to do with frost. It keeps water from a hose lying in a pool, a bucket or a sprayer from being drawn back into the house’s drinking water. The International Residential Code, section P2902.4.3 (quoted here from the City of Seattle’s adopted 2012 text), requires sillcocks, hose bibbs, wall hydrants and other openings with a hose connection to be protected by a vacuum breaker; the ICC’s own CodeNotes points to the same section. The code’s backflow table, P2902.3, lists the frost-resistant, automatic-draining vacuum breaker wall hydrant as its own device, under ASSE 1019.

Two notes from the makers. Legend Valve says it is normal for the vacuum breaker to let some water escape before its piston closes completely, but a continuous stream of water from the bottom of the cap indicates a fouled or failed vacuum breaker. And Woodford’s sheet for its anti-siphon model says an ASSE 1019 device is intended for outdoor watering and shall not be subjected to more than 12 hours of continuous water pressure, one more reason not to leave a hose with a closed nozzle on it.

The same old seals, with a long reach

Inside, a frost-free sillcock is the same washer-and-seat valve described in how a compression faucet works, with a long reach. Woodford’s troubleshooting sheet for its wall faucet sorts the leaks the same way:

• A leak around the stem while the water runs: the packing nut, which sits behind the handle, occasionally needs tightening; a leak that keeps coming back needs new packing.
• A drip from the spout with the faucet off: the seat washer is worn or damaged, or the screw that holds it is loose. If a new washer does not stop it, Woodford says the seat itself may be damaged, and then the faucet needs to be replaced.
• A leak from the vacuum breaker while the water runs: the vacuum breaker is fouled or damaged; Woodford says to check it for fouling or replace it with its vacuum breaker float kit.

Homeowner or plumber

Taking the hose off before the first freeze is homeowner work, and it is what lets a frost-free sillcock of the right length and pitch drain. The American Red Cross list on our October page adds these steps: close the inside valves supplying outdoor hose bibbs, open the outside faucets to let the water drain, and keep the outside valve open so any water remaining in the pipe can expand without breaking it. Snugging the packing nut, and replacing a seat washer, packing or vacuum breaker kit with the maker’s own parts, are homeowner work too, with the water shut off at the valve that feeds the faucet or at the main, following the maker’s sheet. Some makers rule it out: Legend Valve says not to disassemble or service its T-550 and to call a licensed contractor if it malfunctions.

Water in the wall, the basement ceiling or the band joist when the faucet runs usually means a split barrel or a failed joint inside the wall, and that is the line: the repair means cutting into the supply connection on the heated side and setting a new sillcock at the right length and pitch. Call a plumber for that, and for any seat Woodford would have you replace the whole faucet over, unless you already make soldered or threaded water joints with confidence.

Related

• Almanac: October, winterize the outdoor faucets and April, turn the outdoor water back on
• How a compression faucet works covers the washer, seat and packing in a two-handle faucet.
• Glossary: frost-free sillcock, hose bibb, vacuum breaker, backflow preventer, packing nut, seat