Diagram of Water Heater Components

We are all familiar with the humble TPR discharge pipe. This noble valve opens to protect your home from a water heater that is ether too hot or one building up too much pressure. TPR – Temperature Pressure Relief valve. Without this relief valve your water heater can literally become a domestic missile. Just google Myth Busters and Water Heater. Wait… I’ll do it for you.

A very good watch that should have properly scared you into respecting the every day average water heater.

When it comes to the safety features on this rather boring appliance we do not mess around. This is serious business. After your electrical service panel this is the one appliance that can cause actual bodily harm. So, what do we need to know about this TPR discharge pipe?

TPR Discharge Pipes Don’t Share

Two TPR’s on a Single Discharge

Every TPR valve has a discharge pipe. This pipe keeps the emergency evacuation of the water heater directed toward the floor and away from occupants. The last thing you want is for this discharge to be blowing out 218 degree steam at eye level while you’re trying to turn the water off to the appliance.

For this reason it is very important to know if the TPR valve is leaking or not. A TPR valve that leaks IS A PROBLEM. This valve should NEVER leak. As soon as it leaks, it’s time to call a plumber and head this problem off at the pass.

Who do we know if it’s leaking? Water, below the discharge pipe. See what below the pipe, call a plumber. Say it with me. What below the pipe? Call a plumber!

This is why TPR discharge pipes are NEVER permitted to be plumbed along with another plumbing line. It may never share with a condensation discharge, a sink or even another TPR valve! Just flip to IRC P2803.6.1

TPR Discharge Shared with another discharge

IRC P2803.6.1 Requirements of discharge pipe. The outlet of a pressure relief valve, temperature relief valve or combination thereof, shall not be directly connected to the drainage system. The discharge from the relief valve shall be piped full size separately to the floor, to the outside of the building or to an indirect waste receptor located inside the building.

That says it all! Don’t do it. No! Not never!


The TPR valve keeps us safe and we need to know the VERY FIRST instance of it failing. If this pipe is sharing a pipe with another discharge how will we know that it is the TPR that is leaking? Or which TPR is leaking, if two were sharing a discharge. This is one valve that we must always be vigilant of so we can avoid being a new story next to bumper video of the Mythbusters.

If it leaks, call a plumber. And how will you know if it is indeed the TPR valve leaking? Because that is the ONLY valve attached to the discharge pipe.

Also, When the TPR discharges this will cause a massive amount of pressure and heat, anything attached to this discharge pipe is probably going to be damaged in some way.

In Conclusion

The Proper Way to Plumb A TPR – One Valve, One Pipe, No Share

TPR Valve discharge pipes are the long ranger of plumbing discharges. Just a lone cowboy in your basement ensuring that your family stays safe and sound. A catastrophic water heater failure is something that few people will ever experience, truly a once in a lifetime event. This is because we are constantly aware of the safety features they have and make sure that these safety features are never compromised.

When it comes to TPR discharge pipes, no sharing. Because if it leaks, call a plumber. Now… Today!