Direct answer: If a hose bib stays dry by itself but leaks once a hose is attached, the problem is usually at the hose connection, not deep inside the faucet. Start with the hose washer, damaged threads, or a leaking hose bib vacuum breaker before assuming the whole faucet is bad.
Most likely: The most common cause is a flattened or missing garden hose washer, followed by cross-threaded or worn hose bib threads. On some hose bibs, a cracked or stuck vacuum breaker will also leak only under backpressure from a connected hose.
First separate where the water is actually coming from: right at the hose nut, from a cap or vent on top of the spout, or from a split in the faucet body. That one detail usually tells you whether this is a simple seal issue, a vacuum breaker problem, or freeze damage. Reality check: a bad hose washer causes a lot more of these calls than a failed faucet body. Common wrong move: cranking the hose tighter with pliers and chewing up the threads.
Don’t start with: Do not start by replacing the whole hose bib. That is usually not the first fix for a leak that shows up only when a hose is attached.
The leak is right where the hose screws onto the hose bib, and it often gets worse when you tighten it harder.
Start here: Start with the garden hose washer, then inspect the hose bib threads for flattening, burrs, or cross-thread damage.
The hose connection itself may look fine, but water spits or runs from the anti-siphon area once the hose is pressurized.
Start here: Check for a failed hose bib vacuum breaker or debris keeping it from sealing.
Without a hose attached the faucet seems normal, but with a hose on you see seepage from a crack or seam.
Start here: Look closely for freeze damage or a split hose bib body. That usually means replacement, not a washer fix.
Water shows up at the siding, foundation, or inside the wall area when the outdoor faucet is on with a hose attached.
Start here: Stop and treat this as a possible frost-free hose bib leak inside the wall, especially after freezing weather.
A hose bib can seal fine by itself but leak immediately once a hose is attached if the hose-end rubber washer is flattened, cracked, or gone.
Quick check: Unscrew the hose and look inside the female hose fitting. If the washer is split, hard, uneven, or missing, replace it first.
If the hose does not seat squarely, the washer cannot compress evenly and water escapes around the connection.
Quick check: Run a fingertip around the hose bib threads and look for mashed spots, sharp burrs, or threads that force the hose on crooked.
On anti-siphon hose bibs, the vacuum breaker may stay dry until a hose creates backpressure, then it leaks from the top or side vent.
Quick check: With the hose attached and water on, watch the top of the spout. If water comes from the vented cap area, the vacuum breaker is the likely culprit.
A small crack may not show much with an open spout, but hose pressure can force water out of a split casting or back into the wall.
Quick check: Inspect the faucet body closely for hairline cracks and watch the wall area while the hose is pressurized.
A hose-nut leak, a vacuum-breaker leak, and a freeze crack can look similar from a few feet away, but they do not get the same fix.
Next move: Once you know the exact leak point, the next step is usually straightforward. If everything gets wet too fast to tell, disconnect the hose and inspect the hose washer and threads first since that is the most common source.
What to conclude: The leak location tells you whether you are dealing with a simple connection seal problem, a failed hose bib vacuum breaker, or likely freeze damage.
This is the fastest, cheapest fix and it solves a large share of leaks that happen only with a hose attached.
Next move: If the leak stops, the faucet itself was probably fine and the hose connection just was not sealing. If it still leaks at the connection with a fresh washer and straight threads, inspect the hose bib outlet threads closely.
What to conclude: A leak that improves or stops with a new washer points to a sealing issue at the hose connection, not an internal faucet failure.
Good washers still leak when the hose cannot seat flat against the faucet outlet.
Next move: If cleaning and straight hand-threading stop the leak, you likely had debris or a slightly misstarted hose. If the leak remains at the connection and the threads are damaged, the practical repair is usually replacing the hose bib rather than forcing the hose tighter.
A leaking anti-siphon cap is a different problem than a bad hose washer, and it often shows up only when a hose is attached.
Next move: If the vent area stays dry, the vacuum breaker was the failed part. If water still leaks from the body or wall area, or the vacuum breaker is not serviceable, move to the final check and plan for faucet replacement or a plumber.
A hose bib that leaks only under backpressure can have a split body or hidden frost-free damage, and that is where DIY should get more cautious.
A good result: If you confirm the leak is only at a replaceable vacuum breaker or hose washer, you can stop there and avoid a full faucet replacement.
If not: If the source is a crack, hidden wall leak, or badly damaged outlet, the safe next move is hose bib replacement or professional service.
What to conclude: Visible cracking or wall leakage points away from a simple connection repair and toward freeze damage or a failed hose bib assembly.
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Because attaching a hose adds backpressure and creates a seal at the outlet. That exposes problems at the hose washer, outlet threads, or vacuum breaker that may not show when the faucet runs open.
Yes. A cracked hose coupling, missing hose washer, or warped female hose end can make it look like the hose bib is leaking when the real problem is on the hose side.
Usually the washer is worn out, the hose started crooked, or the hose bib threads are damaged. More force rarely fixes that and often makes the threads worse.
That usually points to a leaking hose bib vacuum breaker or anti-siphon assembly. It is different from a leak at the hose nut and often shows up only when a hose is connected.
Not first. Start with the hose washer and thread condition, then check the vacuum breaker. Replace the whole hose bib only if the outlet is cracked, the threads are too damaged to seal, or you confirm freeze damage or a hidden wall leak.
Yes. Freeze damage can leave a small split that only leaks when pressure builds with a hose attached. That is especially common after winter if the hose was left connected.