UPC Section 608: Water Heater Relief Valve and Discharge Pipe Rules

Every water heater must have a combination temperature and pressure relief valve, and that valve must have a discharge pipe run to a safe location. The code is specific about how that pipe is built. It states the core rule directly:

The discharge pipe shall not be trapped, shall be of approved material, shall not be smaller than the outlet size of the valve, and shall discharge to an approved location.

From that flow the details plumbers have to hit. The pipe must be full size, never reduced below the valve's outlet. It must run downhill by gravity so it drains completely and never traps water. It must carry no valve, cap, plug, or reducer anywhere along its length, because any blockage would stop the valve from relieving pressure. It must be approved material rated for hot water, so plain PVC is out. And it must terminate near the floor, generally within about 6 inches, at a drain pan, floor drain, waste receptor, or outdoors, where a release is visible and cannot spray a bystander.

This section governs every water heater install and replacement. Picture a heater in a garage: the relief valve's discharge pipe has to run down the wall and end a few inches above the floor or drain, with nothing capping it. An inspector who sees a discharge pipe that runs uphill, dead-ends inside a wall, or has a shutoff on it will fail the install, because each of those defeats the safety valve. A common mistake is a homeowner adding a cap to stop a nuisance drip, which turns a minor problem into a rupture risk.

If your water heater's relief valve is dripping, do not cap it. A drip usually means the valve is doing its job or the system pressure is too high, and both need a real fix, not a plug. Check that the discharge pipe runs downhill, is full size, and ends near the floor. For how the relief valve fits into the rest of a safe install, see UPC 507 water heater installation and water heater clearance and access code. Because a mistake here is a safety issue, a licensed plumber and a pulled permit are the right call for a water heater swap.

UPC Section 608 is part of the Uniform Plumbing Code. IAPMO publishes and holds the copyright on it. The excerpt above reflects the rule as adopted; Phoenix enforces the 2024 UPC with local amendments, and exact section numbers shift between editions, so verify the current text. Read the discharge-piping rules on UpCodes, or confirm local amendments through the City of Phoenix: phoenix.gov/pdd.