Short answer
A warm spot on a tile or concrete floor almost always means a hot-water line is leaking under the slab. Confirm it by shutting the cold inlet valve on your water heater. If the meter's leak indicator stops, the leak is on the hot side. Leave the water heater's supply off between uses until it's repaired.
Why it happens in Valley homes
Most Phoenix-area homes are on slab foundations with copper hot lines running under the concrete. Hot lines expand and contract every time they're used, and over years they wear against gravel and concrete until a pinhole forms. The escaping hot water warms the slab above it.
How to confirm it
Do these checks before calling so you can tell the plumber what you found.
- Walk the floor barefoot, or use an infrared thermometer, to map the warm area.
- Check the meter's leak indicator with everything off.
- Close the water heater's cold inlet valve and watch the meter again.
- Listen near the warm spot for hissing or running water.
What not to do
Don't start breaking tile to look for it. A leak detection visit pinpoints the spot, and a reroute through the attic may mean no concrete needs to be opened at all.
Repair options
The three options are a spot repair through the slab, rerouting the line through the attic and walls, or a full repipe if the home has had several leaks. A plumber explains which fits your home after detection.
When to call a plumber
- The warm spot is confirmed and the meter moves with everything off.
- Flooring is lifting or baseboards are swelling.
- It's your second or third slab leak.
What the plumber does: see slab leak detection.
Common questions
Is a slab leak an emergency?
It's urgent rather than an emergency: water and energy are lost every hour, and soil under the slab gets saturated. Shut the water heater's supply between uses and book detection soon.
Can I keep using hot water until it's fixed?
Briefly, but it wastes energy and water. Many homeowners close the water heater's cold inlet except when they need hot water.
Editorial note: this guide is general information for Phoenix-area homeowners, not a diagnosis. Conditions vary by home, so a licensed plumber should confirm the cause before any repair.