What is the code for a TPR valve discharge pipe?
Usually full size, gravity drain, no valve, ending within six inches of the floor or over a drain. Plus relief valve, expansion tank and pan costs.
Updated · By 
Ben Sikes
What are the requirements for a TPR discharge pipe?
The International Association of Certified Home Inspectors (InterNACHI) and Omaha's plumbing code agree on the basics for a TPR (temperature and pressure relief) valve discharge pipe. It must be full size, drain by gravity, have no valve on it, and end within six inches of the floor or over a drain. The code your city or county adopted governs your address, so have a licensed plumber price a flagged pipe before your deadline. Price any flagged expansion tank or drain pan on the same visit, then ask the seller to repair them or credit you the plumber's written bid.
Key takeaways
- Pipe material depends on your city. Omaha allows only rigid copper or steel, while InterNACHI's list also includes CPVC and rules out PVC.
- A dripping TPR valve is not a working one. InterNACHI says a leak means the valve needs replacing.
- A pan is needed where a leak would damage finished space, such as an attic or upper floor. A heater on a basement slab with a floor drain typically doesn't need one.
A TPR discharge pipe should drain to a floor drain, an indirect waste receptor, or the outdoors. It shouldn't connect straight into the drain system. Where pipes can freeze, InterNACHI says an outdoor run should first go through an air gap to a receptor in a heated area. It also shouldn't have a trap, since standing water may become contaminated and flow back into the drinking water.
How serious is a bad TPR discharge pipe?
A bad TPR discharge pipe is a safety finding. The valve opens when the tank gets too hot or too pressurized, and the pipe carries that water somewhere safe. If the valve and other safety devices malfunction, InterNACHI says the water can heat past its boiling point, and once the tank ruptures it "will expand into steam almost instantly." That "can propel a heating tank like a rocket through multiple floors, causing personal injury and extensive property damage."
A working valve shoots out a jet of hot water, not a drip. So the pipe must discharge "in a manner that could not cause scalding," in a spot where people will notice it. A leaking valve is a sign it needs replacing.
Send any of these to a licensed plumber before your deadline:
- A pipe that ends high off the floor, or is narrower than the valve outlet.
- A valve anywhere on the pipe, or a threaded end someone could cap.
- PVC pipe, which InterNACHI says can melt, or a material your local code doesn't allow.
Why do you need an expansion tank on a water heater?
You need an expansion tank because water expands as it heats. In a closed system, InterNACHI says, that extra volume "can create dangerously high water pressure," and the tank absorbs it against a cushion of air.
The code ties the need to your supply line. Where a backflow preventer or check valve means heating raises the pressure, the model International Residential Code (IRC) section P2903.4 requires a device to control it, and cities adopt that code locally. InterNACHI notes many jurisdictions now require a tank when a water heater is installed, but some regions don't. A licensed plumber or your building department answers for your house.
An existing tank counts too. InterNACHI says to check it for support, corrosion and leakage. A bladder that has lost some air can be topped up through a valve like a bike tire's, so ask the plumber whether the tank needs air or replacing.
When does a water heater need a drain pan?
A water heater needs a drain pan wherever a leak from the tank would cause damage, under IRC section P2801.6, which cities adopt locally. The pan has to be at least 1 1/2 inches deep and drain through a pipe at least 3/4 inch wide. The same section doesn't require a new pan drain for a replacement heater where none was installed before.
Cost guide WaterHeaterReplaceCost.com reads that as an attic, an upper floor or a finished closet, where a leak would damage finished space. It says a heater on a basement slab with a floor drain typically doesn't need one. Your plumber or building department confirms which applies to your house.
What does it cost to fix a TPR pipe, expansion tank or drain pan?
The cost depends on which part is flagged and whether the heater is being replaced at the same time.
| Item and scope | Source | Cost |
|---|---|---|
| Pressure relief valve replaced by a professional | Bob Vila | $200 to $300 |
| Expansion tank replaced, parts and labor | Bob Vila | $100 to $400 |
| Pan and drain line retrofitted under an existing heater, installed | WaterHeaterReplaceCost.com | $235 to $540 |
| Pan and drain line added during a heater replacement | WaterHeaterReplaceCost.com | $100 to $300 |
Kept prices every line of an inspection report for $79, usually under 4 hours, and marks the ones that need a professional quote.
Say the report flags a corroded, leaking expansion tank and no pan under a heater in an upstairs closet. The tank at $100 to $400 plus a pan retrofit at $235 to $540 comes to $335 to $940. If the discharge pipe is flagged too, add the plumber's price for it.
Correcting the pipe on its own is priced by your plumber's written bid. How to get repair estimates during the inspection period covers getting one before your deadline.
What do I ask the seller for?
Ask the seller for one of two things, in writing:
- Repair before closing. A licensed plumber corrects each item to local code, and you get the invoice.
- A credit. The seller pays the amount on your plumber's written bid.
Name each item, the trade and where your figure came from. The buyer repair request letter template has the wording. What to ask for after a home inspection shows how small items fit with the rest of your list. For the report's other plumbing lines, see plumbing findings on an inspection report.
What if the seller won't fix it?
If the seller won't fix it, decide whether to accept, counter with a smaller credit, or back out. If you stay, book the plumber for your first week in the house and budget the bid. Your contract sets the dates and terms for backing out, so confirm them with your agent.
How do I know what my list is worth?
Your list is worth what each line costs to fix. Send the water heater items to your plumber and let the memo price the rest.
If the water heater is one corner of a longer report, upload your inspection report to Kept and spend your plumber's visit on the lines that need one.
Sources
- InterNACHI, "TPR Valves and Discharge Piping"
- InterNACHI, "Water Heater Expansion Tanks"
- Omaha Plumbing Code Sec. 49-1607, Relief Valves and Settings
- Texas State Residential Code, Board of Plumbing Examiners 2018, P2801.6, Required Pan
- Texas Windstorm Insurance Association Residential Code P2903.4, Thermal Expansion Control
- Bob Vila, "How Much Does Water Heater Repair Cost?"
- WaterHeaterReplaceCost.com, "Water Heater Drain Pan Cost"
Cost figures are modeled from public wage and materials data unless a line says observed. Kept is accountable for the numbers on this page, and corrections go to support@usekept.com. How we price.