Quick Answer:
If the sink stalls after winter work, it’s usually trapped air, frozen debris that loosened, or a partially closed valve. Start by turning water back on fully and flushing the lines. If that doesn’t clear the problem, check the trap and run a snake or a thorough flush before calling a pro.
Why This Happens
Winterizing and then returning plumbing to service can trap air, dislodge mineral deposits or bits of insulation, and leave shut valves partially closed. Pipes that were partially frozen can shed rust or scale when thawed, and that material can lodge in the P-trap or near the tailpiece. Vents that were blocked or seals that were disturbed can also change flow and make standing water back up into the basin.
For related drainage patterns you may want to read about Sink fills during storms and how shared drains behave, or troubleshooting when a sink backs up with other fixtures like the shower—see Sink backs up only when bathtub drains.
Step-by-Step What to Do
1. Confirm valves and water supply
- Make sure individual shutoff valves under the sink and the main supply are fully open.
- Open both hot and cold taps to let air escape and to see whether flow is steady.
2. Flush drains thoroughly after winterization
- Run hot water at full flow for several minutes to help move loose debris and dissolve any grease or residue.
- Flush with cold water afterward to clear remaining particles.
- Also run nearby fixtures (toilet, shower) for a short time to help move material through shared drain lines.
3. Check and clear the P-trap
- Place a bucket under the trap, loosen the slip nuts, and inspect for debris. Clean out any gunk or particles.
- Reassemble carefully and run water to test.
4. Use a plunger or small drain auger
- Try a sink plunger first (create a seal over the drain). Several firm pumps can dislodge air pockets or small clogs.
- If that fails, use a hand auger (snake) sized for sink drains to reach obstructions beyond the trap.
5. Test venting and adjacent fixtures
- Run the bathtub or another nearby fixture to see if backups change. This helps identify shared-line problems.
- Note abnormal gurgling or slow draining, which can mean a vent issue or a deeper blockage.
6. Re-check after a full flush
- After cleaning and any snaking, run several minutes of hot then cold water again to ensure the line is clear and air is purged.
What Not to Do
- Do not ignore debris after winterization. Leaving loose material in the system will cause repeat clogs and may damage traps or valves.
- Do not pour large amounts of chemical drain cleaner into a sink where you plan to use a snake or where you suspect a recent seal or rubber part—chemicals can burn skin and damage pipes.
- Do not force fittings or overtighten plumbing joints when reassembling the trap; strips and cracks can cause leaks.
When to Call a Professional
- Water still backs up after you’ve flushed lines, cleared the trap, and tried a plunger/snaking.
- Multiple fixtures are affected or there is sewage backup—this often means a main line or sewer issue.
- You detect foul sewage odors, persistent slow drains, or you’re uncomfortable taking apart plumbing components.
Safety Notes
- Shut off water at the nearest valve before disassembling the trap to avoid spills.
- Wear gloves and eye protection when removing debris. Wash hands after handling plumbing parts.
- Avoid mixing chemical cleaners with manual tools. If chemicals were used, ventilate the area and follow label safety instructions; do not snake a drain immediately after pouring chemicals.
Common Homeowner Questions
- Why did this start right after winterizing? Air pockets or dislodged buildup from thawing and turning the system back on are common causes.
- Will running hot water always fix it? Often a good flush clears small debris and air, but stubborn clogs need physical removal.
- Can I use an electric snake myself? If you’re inexperienced, avoid powered tools—hire a pro to prevent damage to pipes or fixtures.