Quick Answer:
You likely have a frozen section, a blockage, or a shifted pipe after thawing. First check exterior cleanouts and remove any winter caps, then gently run warm water in nearby fixtures to see if flow returns. If thawing reveals leaks or a burst pipe, shut off the main water and call a plumber to avoid water damage.
Why This Happens
Pipes that were winterized can still hold pockets of water. When you turn the heat back on, those pockets thaw and can create sudden pressure or dislodge blockages. Ground movement from frost heave can shift underground lines or cause roof vents and stacks to crack. Any shift, crack, or remaining ice plug may cause backups when flow resumes.
For related troubleshooting and cases where a disposal is involved, see the cluster hub topic Sink Backs Up When Disposal Runs. If you want background or similar scenarios, refer to the peer notes such as Backup after winterization and Backup after long vacation.
Step-by-Step What to Do
Step 1 — Stop using affected fixtures and check exterior cleanouts
- Turn off any faucets or appliances tied to the affected drain to avoid adding water to a backup.
- Locate exterior cleanouts (usually capped pipes near the foundation or at grade) and remove any winter caps you installed so the line can vent and drain.
Step 2 — Look for signs of frost heave or roof vent damage
- Walk your yard and check the foundation for uneven settling or raised soil—signs of frost heave that can stress underground pipes.
- From the ground (or have a pro check the roof), look for cracked or displaced plumbing vents; a cracked vent stack can trap air and affect flow.
Step 3 — Gently thaw nearby fixtures
- Open a nearby cold and warm faucet slightly and run warm (not scalding) water to see if flow returns.
- Apply gradual warmth to accessible sections (for example, use warm towels or a hair dryer on low at a safe distance). Never use open flame or high-heat devices.
Step 4 — Inspect for leaks as things thaw
- Watch walls, ceilings, floors, crawl spaces, and the pipe run itself as ice melts. If you see dripping or swelling, shut the main water supply immediately.
- If a section that was frozen begins to leak or gush, keep the main off, contain water with towels or buckets where safe, and call a plumber to prevent damage.
Step 5 — If flow returns, verify full drainage
- Run water long enough to clear any remaining debris. If a single fixture still backs up, try a plunger or small hand auger only if you are comfortable and the pipe is accessible.
- If multiple fixtures are slow or backing up, don’t keep pushing water into a possibly damaged or blocked sewer—call a pro.
What Not to Do
- Don’t use a torch, propane heater, or any open-flame or high-heat device to thaw pipes—this is a fire and pipe-damage risk.
- Don’t pour extremely hot or boiling water into a cold trap or directly onto frozen pipes—sudden temperature change can crack fittings or porcelain and make leaks worse.
- Don’t delay calling a professional when you suspect a frozen or burst section, when thawing reveals leaks, or when backups began immediately after winterization steps—those are signs you need trained help.
When to Call a Professional
- There is visible leaking, wet drywall, warped flooring, or water in ceilings.
- You locate a burst or cracked pipe, or thawing produces a sudden leak.
- Multiple fixtures back up or you can’t locate the frozen section. Also call if backups started right after winterizing or de-winterizing steps and you’re unsure what changed.
Safety Notes
- If you shut the main, make sure everyone in the house knows and that appliances expecting water are turned off.
- Keep electrical devices and outlets away from pooled water. If water reaches electrical panels or outlets, turn power off at the breaker and call an electrician.
- Use personal protective equipment (gloves, eye protection) when handling contaminated water from backups.
- When in doubt about structural damage, roof work, or sewer lines, hire a licensed plumber—attempting risky repairs yourself can make things worse.
Common Homeowner Questions
- My drain was frozen—can I force it with a lot of water? No. Adding large amounts of water can flood the area if the line is blocked or damaged.
- How fast should I call a plumber after thawing shows a leak? Immediately—shut the main and call as soon as you see dripping or leaking to limit water damage.
- Will a plunger help if multiple fixtures back up? Unlikely. Multiple backups usually indicate a main line or sewer problem that needs a pro.