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Building Code Reference

Got a CPC 504.0 correction?

Water heater T&P valve

For builders in California, Greater Seattle, the Las Vegas area, the Denver area and Kansas City · CrossBeam Permits

What this code requires, how to fix it, and how cities and counties review it

What this code requires

CPC 504.0 requires every water heater to have an approved temperature and pressure (T&P) relief valve, and that valve must have a discharge pipe that routes the hot water safely to the exterior. The discharge pipe must be rigid, slope continuously downward without any horizontal traps or valves, terminate between 6 inches and 24 inches above the floor or ground, and have an open, unthreaded end. It cannot discharge inside the living space, into a wall cavity, or into a water heater drain pan.

How to fix it

  1. Locate the water heater on your plans

    Find every sheet where the water heater appears: site plan, floor plan, plumbing plan, and any detail sheets. The T&P discharge pipe must be shown consistently on all sheets. If the heater only shows up on one sheet, that is usually where the correction gets missed.

  2. Add a T&P discharge pipe to the plumbing plan

    Draw the discharge pipe from the T&P valve on the water heater to the exterior of the building, or to an air gap into the drainage system. Show the pipe as a rigid line, not a flex connector. Label it "T&P relief valve discharge pipe" so the plan-checker knows what it is. The pipe must slope downward continuously from the valve to the termination point.

  3. Show the termination point on the exterior elevation

    On the exterior elevation or site plan, mark where the discharge pipe exits the building. The open end must be between 6 inches and 24 inches above the floor, ground, or grade at that point. Add a dimension note: "T&P discharge pipe termination, open end, 6 inches min to 24 inches max above grade." The plan-checker will verify this note against the elevation.

  4. Specify rigid pipe material rated for T&P discharge

    Note the pipe material on your plans. The code requires discharge piping rated at not less than the operating temperature of the system and approved for the use, or complying with ASME A112.4.1, and no smaller than the valve outlet. Copper and galvanized steel are common choices; flexible braided connectors are a common flag. Verify with your local building department which plastic pipes, such as CPVC or PEX, it accepts for this application.

  5. Show open, unthreaded pipe end

    Add a note or detail showing the terminal end of the pipe is plain-cut and open. No caps, no plugs, no threaded fittings at the end. A threaded end reduces the flow area and can accumulate mineral deposits that restrict the opening. The note can be as simple as "T&P discharge pipe: open, non-threaded end, field verify clearance to grade."

  6. Route away from gas valves and electrical panels

    The discharge pipe should not terminate directly above a gas meter, gas shutoff, electrical panel, or any opening into the building. If the geometry of the installation requires routing past these elements, add a note showing the pipe terminates away from them. Plan-checkers sometimes flag layouts where a T&P discharge directly above a gas regulator would create a hazard if the valve opened under pressure.

  7. Keep the T&P discharge out of the drain pan

    CPC 608.5 and 507.5 prohibit relief valve discharge into a water heater pan, even one with a drain. Run the T&P line on its own to the exterior or through an air gap into the drainage system. If the heater needs a pan (attic or over a floor-ceiling assembly), show the pan separately with its own 3/4-inch drain to an approved location and a readily visible end. A T&P line ending in the pan will be rejected.

  8. Verify no valves or traps interrupt the discharge path

    The T&P discharge pipe cannot have any shutoff valves, check valves, or traps between the relief valve and the termination point. These devices block the flow path in a real discharge event. Add a note to your plans: "No valves or traps on T&P discharge line." If your current design has a union for serviceability, that is acceptable, but a shutoff valve is not.

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Why you got flagged

Plan-checkers flag CPC 504.0 most often because the T&P discharge pipe simply does not appear on the plans at all. A water heater gets drawn in the garage or utility room with a gas line and a cold-water supply, and the discharge pipe gets left off the sheet. The plan-checker sees a valve with nowhere to go and marks it as a corrections item. This is the single most common reason this section comes back on a corrections letter.

The second scenario is a routing problem. The pipe is shown on the plans, but it terminates inside the building or into a drain pan. Plan-checkers will reject any routing that leaves hot water with nowhere to go if the valve opens. Discharge into a water heater pan is prohibited outright, even if the pan has its own drain.

Another common flag is a threaded discharge pipe termination. The end of a T&P discharge pipe must be plain-cut and open so water flows freely. A threaded cap or fitting at the end restricts flow and defeats the safety purpose of the valve. If the plans show a threaded end or if the note on the plans says "terminate per manufacturer" without specifying open-end, that will get flagged.

Finally, slope and material conflicts catch plans that specify flexible water heater connectors or plastic tubing for the discharge run. The pipe must be rigid, rated for the discharge temperature, and continuously sloped. PEX or braided flex lines do not meet this requirement on the discharge side.

The official code

California Plumbing Code Chapter 5 — Water Heaters (Building Standards Commission)

Read the source →

Common questions

Can the T&P discharge pipe terminate inside the garage?
Not as an open pipe end. The discharge pipe must discharge by gravity outside the building, or through an air gap into the drainage system (CPC 608.5). Ending the pipe in the garage or any occupied or enclosed space without that air gap connection is not compliant. The reason is safety: a T&P valve opens when water pressure or temperature reaches a dangerous level, and the discharged water or steam must go somewhere that does not pose a burn risk to occupants or create water damage inside the structure.
What pipe material is required for the T&P discharge line?
The discharge pipe must be rigid and rated to handle the discharge temperature from a T&P relief valve. Copper and galvanized steel are universally accepted. CPVC is accepted in most California jurisdictions if the pipe is rated for temperatures up to 210°F. PEX tubing and flexible braided connectors are not accepted for T&P discharge because they cannot handle a full-pressure, high-temperature discharge event. Check with your local building department on CPVC if that is your preferred material.
How high above the ground does the T&P pipe need to terminate?
The open end of the discharge pipe must be between 6 inches and 24 inches above the floor or grade at the point of termination. Too low and the end gets buried or obstructed; too high and someone could get burned by the discharge without warning. Measure from finished grade or slab to the cut end of the pipe. Add a dimension note to your plans so the plan-checker can confirm compliance without a field visit.
Can I put a cap on the end of the T&P discharge pipe to keep bugs out?
No. Any cap, plug, or threaded fitting on the end of the discharge pipe restricts flow and defeats the safety function of the T&P valve. The end must be plain-cut and open. If insect intrusion is a concern, some installers use a loose plastic bug screen, but even that is questionable depending on the inspector. The code is clear that the end must remain open and unobstructed at all times.
Does CPC 504.0 apply to tankless water heaters?
CPC 504.0 applies to water heaters that operate under pressure, which includes most tankless units. Tankless heaters that are truly condensate-only or heat-exchanger-only types without a pressurized water storage vessel may have different requirements. In practice, if you are installing a tankless unit with a pressurized water supply passing through it, you still need to confirm with your plan-checker whether a T&P discharge pipe is required or whether the manufacturer specifies an alternate pressure-relief path. Do not assume tankless means no T&P requirement.
Can the T&P discharge pipe have an elbow or turn?
Yes, the pipe can have elbows and turns as long as the overall path slopes continuously downward from the valve to the termination point. No upturns, no horizontal runs that could trap water, and no sections that slope back toward the valve. The key test is that the pipe must drain completely by gravity so mineral scale does not accumulate in the line. A single 90-degree elbow to get through a wall to the exterior is fine as long as the section after the elbow slopes down to the termination point.
What if my water heater is in an upstairs utility closet with no direct exterior wall?
This is a real headache on multi-story projects and ADUs. You have two options: run the discharge pipe through the floor system to a termination point at the exterior at grade level, or route it to an approved indirect waste receptor such as a laundry sink or floor drain that has a confirmed exterior drain path. Either way, show the full routing on the plans. Pipe runs that go through multiple floors attract close scrutiny, so call it out clearly with a pipe routing diagram and confirm the slope throughout.

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