Hot line or cold line: identify which pipe is leaking
Closing your water heater cold-inlet valve and rechecking the meter gives a definitive answer. If you have not run that test yet, answer the symptom questions below for a best-guess verdict instead.
Answer these
Your result
undetermined
Why
Close your water heater's cold inlet valve and recheck the meter for a definitive hot-versus-cold answer.
This tool is a guide, not a diagnosis. It never asks you to open a slab, cut pipe, or touch gas or electrical. Confirm any leak with a licensed plumber.
Assumptions
- •This tool assumes a standard single water heater with an accessible cold-inlet shutoff valve.
Questions this tool answers
Why is the valve test more reliable than the symptom questions
Closing the water heater cold-inlet valve physically isolates the hot line from the rest of your plumbing. If the meter stops, the leak has to be on the hot side; if it keeps moving, the leak has to be on the cold side. Symptoms like warm floors are common with hot-line leaks but are not definitive on their own.
Why are most slab leaks on the hot line
Hot water lines expand and contract more than cold lines every time the water heater cycles, which speeds up wear at pipe joints and any weak point in copper or galvanized pipe under the slab.
What do I do once I know which line is leaking
Use the repair method finder next. Knowing hot versus cold does not change whether a plumber recommends spot repair, reroute, epoxy lining, or repipe, but it helps them plan the fix and narrow where to search.
Where is the water heater cold-inlet valve
It is the shutoff valve on the pipe feeding cold water into your water heater, usually within a foot or two of the tank. Closing it stops new cold water from entering the heater without shutting off hot water already in the tank.