Cold water runs lukewarm at the faucet

Symptoms

• Cold tap never gets fully cold
• Problem worse in summer or in a warm crawlspace/attic
• Only one faucet affected versus the whole house
• Cold water takes unusually long to cool down when run

Likely causes

• CommonHot and cold supply lines running close togetherHeat can transfer from an insulated or nearby hot line to the cold line.
• CommonSingle-handle cartridge bleeding hot into cold internallyA worn cartridge can let a small amount of hot water mix in even when set to cold.
• PossibleWarm ambient temperature in the pipe runPipes running through a hot attic or exterior wall pick up heat.
• PossibleNaturally warmer ground/incoming water temperatureMore common in hot climates during summer.

What to do

1. Run the cold water for a couple of minutes to see if it eventually cools down, which points to pipe location rather than the faucet itself.
2. Check if the problem happens at multiple faucets in the house or just one.
3. If it's just one single-handle faucet, the cartridge may be the cause; turn off water and inspect or replace it.
4. If it's throughout the house and worse in summer, the issue is likely pipe routing or ambient heat rather than something to repair at the faucet.
5. Consider insulating hot water pipes if they run close to cold lines in an accessible area like a basement.
6. If it's a single faulty cartridge, replacing it should resolve the mixing.

Tools and parts

• Pipe insulation (if applicable)

When to call a pro

Call a plumber if cold water is warm at multiple faucets throughout the house, since it may point to pipe routing that's harder to fix without their help.

Safety