Symptoms
- Hot side handle gives cold water and cold gives hot
- Started right after a faucet install or repair
- Single-handle faucet feels 'backwards' when adjusting temperature
- Only one faucet in the house is affected
Likely causes
- CommonSupply lines connected to the wrong shutoff valvesHot and cold lines under the sink got swapped during installation or a repair.
- CommonCartridge installed rotated 180 degreesSingle-handle cartridges can be installed backward, reversing the temperature direction.
- PossibleMislabeled shutoff valvesValves themselves may be plumbed to the wrong supply at the wall.
- Less commonFaucet body has reversible hot/cold ports installed incorrectlySome faucet designs allow this and can be assembled wrong.
What to do
- Turn off both shutoff valves under the sink before working.
- Trace each supply line from the valve to the faucet to see if the hot and cold lines were crossed.
- If crossed, disconnect both lines at the faucet or valve and reconnect them to the correct side.
- For a single-handle faucet with correct supply lines, remove the handle and check if the cartridge is oriented correctly per the manufacturer's diagram.
- Rotate the cartridge 180 degrees if it was installed backward, then reassemble.
- Turn the water back on slowly and test hot and cold at both extremes of the handle.
- If it's still reversed, double-check the valves under the sink are actually connected to the correct hot and cold supply from the wall.
Tools and parts
- Adjustable wrench
- Screwdriver
When to call a pro
Call a plumber if the wall-side supply itself seems to be mislabeled, since that may require checking further back in the plumbing.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.