Every September, our dispatch board fills up with the same call: a homeowner who left their irrigation system running through the first cold snap and woke up to a cracked backflow preventer or a hose bib spraying water into a crawl space. It’s rarely a hard freeze that does the damage — it’s the first one, the one nobody was watching for because it showed up three weeks earlier than expected.
That’s the part most “winterize your sprinklers” articles get wrong for this region. They’re written for climates with a predictable frost date and a long, steady cool-down. Western Oregon and Washington don’t work that way. We can run 80°F afternoons in late September and then drop to 28°F overnight a week later when a cold system pushes down from the Gorge or off the coast. Your irrigation system doesn’t get a grace period to catch up — it needs to already be ready.
This is the checklist our licensed plumbers actually use when we winterize irrigation systems and outdoor plumbing for clients from Vancouver and Portland out to Camas, Battle Ground, and the Longview-Kelso area. Work through it over a weekend in September, before the first real cold snap, not after the forecast tells you to.
1. Map every hose bib and irrigation zone before you start
Walk the full perimeter of the house and yard with a notepad or your phone. Most homes we service have three to six exterior hose bibs — front, back, garage, and often one tucked near a side gate or deck that owners forget exists until it splits open in January. Note each one, plus every irrigation valve box and zone controller. You can’t winterize what you haven’t found.
Field note: The bib people forget most often is the one behind shrubs planted after the sprinkler system went in. If your landscaping has changed since you moved in, budget extra time to search — that’s usually the pipe that bursts.
2. Disconnect, drain, and store every garden hose
A hose left attached to a frost-free hose bib defeats the entire point of a frost-free bib — more on that below. Disconnect each hose, drain it fully by stretching it out downhill or coiling it loosely to let gravity pull the water out, and store it somewhere above freezing. Trapped water in a coiled hose left outside will freeze, expand, and split the hose wall even if it never touches your plumbing.
3. Identify whether you have frost-free or standard hose bibs
This single distinction changes everything else on this list, and most homeowners have never checked.
| Type | What to look for | What it needs before fall |
|---|---|---|
| Frost-free (sillcock) | The valve stem runs 6–12″ back into the wall; the shutoff happens inside the heated structure, not at the spigot face. | Just disconnect the hose. Water drains out of the long stem automatically once there’s no hose trapping pressure at the tip. |
| Standard bib | Shutoff valve sits right at the exterior wall — common in homes built or plumbed before the 1990s, and on utility/laundry room spigots. | Needs an interior shutoff closed and the line drained manually, plus an insulated cover for the winter. |
If you’re not sure which you have, that’s a five-minute question for a plumber and worth asking before the first freeze rather than after a pipe splits behind your drywall. Our faucet and fixture team can also swap an aging standard bib for a frost-free sillcock during the same visit — it’s one of the more cost-effective upgrades we install heading into fall.
4. Shut the interior valve and drain standard bibs
If you have standard hose bibs, locate the dedicated shutoff valve inside — typically in the basement, crawl space access, or garage ceiling near where the pipe penetrates the exterior wall. Close it, then go back outside and open the hose bib to let residual water drain and relieve pressure in the line. Leave the outside spigot cracked open through winter; a closed bib with no water behind it does no harm, but a bib that’s closed while trapping a slug of water is exactly what splits fittings.
Common mistake we see: Closing the interior valve and stopping there. Without opening the exterior spigot afterward, the trapped water between the two valves has nowhere to go when it freezes — and it will still crack the pipe.
5. Blow out the irrigation lines with compressed air
This is the step homeowners most often skip or do incorrectly, and it’s the one most likely to cause an expensive break if rushed.
- Shut off the water supply to the irrigation system at the backflow preventer or main irrigation valve before connecting a compressor.
- Connect the compressor to the system via the blow-out port (or the backflow preventer test cock if no dedicated port exists) using the correct fitting — never a standard hose thread crimped on, which can blow off under pressure.
- Open one zone at a time, starting with the zone farthest from the compressor, and run air until only mist comes out of the heads — typically 30–60 seconds per zone.
- Watch your PSI. Spray-head zones can generally take 50–65 PSI; drip and micro-irrigation zones should stay under 40 PSI or the emitters can be damaged. Never exceed the rating printed on your backflow device or valves.
- Wear eye protection. Heads can pop and spray debris under compressor pressure.
Safety note: A shop-vac is not a substitute for a proper compressor blow-out on anything but the smallest drip systems — it won’t generate enough sustained pressure to clear a full zone, and undersized compressors that overheat trying to compensate are a common cause of failed attempts. If you don’t already own a compressor rated for this, it’s usually cheaper to have a technician do the full system in one visit than to buy or rent equipment for a once-a-year job.
6. Insulate the backflow preventer and any exposed piping
Backflow preventers are required on irrigation systems throughout Oregon and Washington to keep lawn chemicals and stagnant water from siphoning back into your drinking water supply, and they’re also the single most freeze-vulnerable component in the whole system because they typically sit above ground. Wrap the device in an insulated cover made for backflow preventers — not just a trash bag or towel, which trap moisture against the housing and can make things worse. Leave the drain ports and test cocks accessible rather than sealing them airtight.
If your backflow preventer hasn’t had its annual test, fall shutdown is a good time to schedule it alongside a general plumbing check — our maintenance service covers both in one appointment.
7. Reset the irrigation controller — don’t just switch it off
Here’s where Pacific Northwest advice really diverges from the national playbook. In much of the country, “winterizing” means shutting the system down for good in September. Here, a dry August can easily run into a dry September, and new sod or fall plantings often still need scheduled water into October. Rather than powering the controller off entirely, switch it to rain mode or reduce run times, and keep an eye on actual rainfall. Do the full water shutoff and blow-out described above once you’re confident the irrigation season is genuinely over for your specific landscaping — not on a fixed calendar date.
8. Walk the whole system once more, looking for slow leaks
Before you close everything up for the season, spend ten minutes checking for damp soil around valve boxes, drips at hose bib connections, and soft or spongy patches near buried lines — all signs of a slow leak that a summer of watering can mask but a freeze-thaw cycle will turn into a real break. This is also a good moment to glance at your water meter with everything indoors shut off; if it’s still ticking, something outdoor is running. Our leak detection service uses acoustic and thermal equipment to pinpoint exactly where a hidden leak sits, without digging up the whole yard to find it.
9. Confirm you know where your main water shutoff is
This takes thirty seconds and matters most on the one night you actually need it. If a hose bib or irrigation line does split during a cold snap, being able to shut off the home’s main water supply immediately is the difference between a mop and a claims call. If you’ve never located yours, or it’s painted over, seized, or otherwise unreliable, that’s worth fixing now rather than during an active leak — it’s a quick item for our pipe repair team to inspect and replace if needed.
Where Oregon and Washington homes differ from each other
Elevation and distance from the Columbia River gorge matter more than which side of the state line you’re on. Vancouver, Portland, and the lowland stretch along the I-5 corridor tend to see their first hard freeze later and milder than higher-ground areas nearby. Homes in Camas, Washougal, Battle Ground, and especially Cougar sit closer to the foothills and the Gorge wind corridor, and routinely see frost — and gorge-driven cold snaps — one to three weeks earlier than homes down in the valley. If you’re in one of those areas, move this whole checklist up on your calendar rather than waiting for a Vancouver-based forecast to tell you it’s time.
When to call a licensed plumber instead of doing it yourself
Most of this checklist is genuinely DIY-friendly with basic tools. Call a professional if any of the following apply:
- You don’t have a compressor rated for a full-system blow-out, or you’re not confident about safe PSI limits for your specific heads and drip lines.
- Your backflow preventer is due for its annual test, or you’re not sure it’s ever been tested.
- You found a standard hose bib you’d rather replace with a frost-free sillcock before winter.
- You’ve had a pipe freeze and crack in a previous winter — that’s usually a sign of an underlying insulation or routing issue, not bad luck.
- Anything already looks wet, soft, or damaged when you do your walkthrough.
And if a line does let go on a Friday night in the middle of a cold snap, that’s exactly what our 24/7 emergency plumbing line is there for.
Ready for fall? Let’s get your system shut down right.
Our licensed plumbers can blow out your sprinkler lines, test and insulate your backflow preventer, and check every hose bib on the property in a single fall visit — so you’re not troubleshooting a burst pipe on the coldest night of the year. We serve Vancouver, Portland, and communities throughout Clark County and the greater Cascade footprint. Book a fall plumbing check online or call us at (360) 726-5181.
Related reading: Summer Plumbing Prep for Portland & Vancouver Homeowners · Plumbing Maintenance Services · Leak Detection Services · Residential Plumbing Services
Kevin Sayles owns and operates Cascade Northwest Plumbing, serving Vancouver, WA, Portland, OR, and the surrounding Clark County and Columbia River communities. Learn more about our team.