My tankless water heater (located in the basement) has the TPR valve discharge pipe traveling upwards, which is against code, and it terminates into the soil outside the house.

What is the best way to rectify this?

Other Notes: No sump pump, no floor drain. In California.

It seems like a 5 gallon bucket wouldn’t be capable of handling the flow, so I’d still like to have it go outside, but that doesn’t seem possible without having the piping go upward at some point (which is against code). Installing a floor drain seems excessive (and expensive).

  • I have never heard of a TPR valve on a tankless water heater. Is this a California code? what is the function of a TRP on a tankless?
    – Alaska Man
    Aug 18, 2019 at 17:21
  • @Alaska Man The standard set of hardware for installation of a tankless water heater includes a pressure relief valve. It fits on the hot water output. For example homedepot.com/p/… Aug 18, 2019 at 20:12
  • This may be irrelevant for the OP's question, but the relief valve for a tankless water heater is a pressure relief, not a temperature-pressure relief. In the case of a tank, the temperature sensor protrudes into the tank and would detect overheating of the whole tank whereas in the tankless the relief valve is on the outlet after the heat exchanger so a runaway burner (with the flow off) would develop damaging over-pressure before the water in the outlet would get hot. Hence maybe there would be no point in having a temperature sensor. But what about a runaway with flow on?! Aug 19, 2019 at 3:24

2 Answers 2


TPR piping has one solitary purpose, and that is to relieve pressure should a problem arise that overpressures or boils water in the heater. Such a problem could include the city supply overpressuring for some reason. The discharge will be steam or water, and it needs to discharge somewhere (preferably: safe).

The discharge could be massive since it is fed off main supply.

Even if a bucket met statute, it would quickly overflow and cause a flood event in your home, and that means you'd get to have the guys with the industrial dehumidifiers come out and spend a week busting out drywall and flooring, and unfinishing your basement, then fun with the insurance company. Goodee.

So that piping should "go overboard" to somewhere non-destructive, like a downspout on a downhill side of the house.

The only bad thing about going upward is after the event ends, stagnant water could be trapped in the rise. The installer should have never installed your water heater oriented like that. But these events are quite rare, and are usually the death rattle of the water heater, so I wouldn't worry about it too much.


If you're serious about correcting the problem you could get a 10 gallon tank, bucket, capable of handling 210 degrees F. and a hot water circulating pump with a float activation switch. the TPR valve discharges water into the bucket, the float switch activates the pump, the pump pumps the water out the piping that it already there going outside. These pumps run on 120V and pump 13 gallons per minute. Good luck


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