Quick Answer:
If multiple drains back up after you turn the water back on, stay calm and follow a short checklist: confirm valve positions used for winterization, open outdoor valves to bleed lines, run one low-flow test at a single fixture while watching for leaks, and inspect accessible pipe runs for splits or wet insulation. If you find a broken pipe, shut off the main water immediately and call for help.
Why This Happens
When plumbing is reactivated after winter, trapped air, settled debris, or partial thawing of ice can cause slow or reversed flow in drain lines. Valves left in the wrong position can isolate parts of the system, forcing water into other drains. Pipes that were frozen may have small splits that leak or allow water to pool in insulation, creating backups.
These situations can mimic other problems you may have seen before — for example, check related issues like Backups after water heater install and consider whether similar flow or venting problems could apply to your home.
Step-by-Step What to Do
1. Confirm valve positions
Find your winterization notes or checklist. Go through each isolation valve (supply shutoffs to zones, water heater bypasses, and appliance valves) and set them exactly as noted for normal operation. A single valve left closed can reroute flow and cause multiple backups.
2. Open outdoor hose bibs and frost‑proof valves
Open all outdoor hose spigots and any frost‑proof valves to bleed air and any remaining antifreeze from outside lines. Leave them open until water runs clear and sputtering stops. This releases trapped air that can cause strange pressure and flow behavior inside the system.
3. Run a single low‑flow test at one nearby fixture
Choose one easily observed fixture (a sink in a utility room or laundry). Turn it on at a low flow for a short time while watching visible pipe runs, joints, and insulation for leaks or condensate. Do this rather than turning on multiple fixtures at once.
4. Inspect accessible pipes for splits or damp insulation
- Look along basements, crawlspaces, and interior walls for wet insulation, soggy drywall, or visible pipe splits.
- Check under sinks and around appliance connections where frozen pipes were likely.
If you find damp insulation or a small split, shut off water to that area if possible and prepare to shut off the main if the leak gets worse.
5. Shut off the main immediately if a pipe is broken
If you see a clear rupture, active spraying, or rapidly soaking insulation, turn off the main water valve at once to limit damage. After shutting the main, open a nearby drain to relieve pressure and call for emergency repair help.
What Not to Do
- Don’t force high water pressure to “blast” frozen debris through pipes—this can cause ruptures and make a small problem much worse.
- Don’t ignore signs of serious damage. Don’t delay — call a pro when you see wet ceilings, persistent backups, or visible pipe splits after thawing.
When to Call a Professional
Call a licensed plumber immediately if any of the following occur:
- Visible pipe splits, active spraying, or rapidly expanding wet areas.
- Wet ceilings, bulging drywall, or water entering living spaces.
- Persistent backups after you’ve confirmed valves and bled lines.
For intermittent or unclear symptoms (for example, if drains act up now and then), consider professional diagnosis — it’s similar to other flow problems like Multiple drains back up intermittently and a pro can test vents, traps, and hidden lines safely.
Safety Notes
- Turn off electricity to areas with standing water before working near outlets or fixtures, or keep clear until a qualified professional can help.
- Avoid standing on ladders under wet ceilings; wet drywall can collapse and cause injury.
- When shutting the main, have towels and buckets ready and move valuables away from likely drip areas.
Common Homeowner Questions
- Why did several drains back up at once?
Air, trapped debris, or wrong valve positions after winterization are common causes. - Can I just run all faucets to clear the system?
No—start with a single low‑flow test. Running many fixtures can hide a leak and increase the risk of a rupture. - How fast should I call a pro?
Call immediately for visible leaks, wet ceilings, or backups that don’t clear after basic checks.
More in this topic
For more related fixes and similar symptoms, see Multiple Fixtures Backing Up Together.