Navien npe 240 pressure relief valve leaking

[Baltik]

I have a 150psi pressure relief valve and a small expansion tank (http://zilmetusa.com/Thermal-ZEP1)
I noticed some wetness around the relief valve and went ahead and replaced it. However the same activity is happening, small water releases from the pressure relief valve after use. Is this normal behavior? what's the best way to troubleshoot if not

 

[Sylvan]

If the T&P seeps it is pressure If it fully opens the water temperature exceeded 210 deg


Check the pressure of the cold water supply

 

[Sponsor]

 

[John Gayewski]

Your expansion tank had gone bad. That is the most likely cause.

 

[Breplum]

Start with what Sylvan said: check pressure. You need to purchase or borrow a gauge that has a hose bibb connection. It is a common item. It should have a range up to 200 psi.

 

[Bannerman]

When obtaining a pressure gauge, suggest obtaining one equipped with a 2nd pointer to indicate peak pressure. Because you may not be viewing the gauge when the pressure is highest, the 2nd pointer will indicate the highest pressure sensed after the pointer was last manually reset.
Gauge example: http://modusgauges.com/special-purpose-instruments/peak-/-max-pressure-gauges/cat_29.html

 

[John Gayewski]

We know the pressure is spiking. Why do we need to measure it? Check the expansion tank.

 

[Baltik]

the tank is adjustable at 50psi - would it make sense to try 75 while i wait to source a gauge? also where should said gauge be hooked up?

 

[John Gayewski]

the tank is adjustable at 50psi - would it make sense to try 75 while i wait to source a gauge? also where should said gauge be hooked up?

The tank needs to be checked to see if it's broken. That's the first thing.

 

[Reach4]

the tank is adjustable at 50psi - would it make sense to try 75 while i wait to source a gauge? also where should said gauge be hooked up?

A laundry tap or the drain line on a tank WH would be common places to hook a garden hose thread pressure gauge. If you know the outside hose bib is not before a pressure reducing valve you could go there. I don't if a tankless WH would have a tap with a garden hose thread.

These gauges should be readily available at a hardware store, big garden shop, or a home improvement store. Under $20, and often well under. Zero to 200 psi should fit your needs.

 

[Reach4]

We know the pressure is spiking. Why do we need to measure it? Check the expansion tank.

I was thinking maybe tankless WHs did not need expansion tanks. I was apparently wrong. Maybe smaller ones would do the job. Plus, I guess some "tankless" units have little tanks.

Baltik, do you have a thermal expansion tank? Those should normally be empty of water, unless you just used a bunch of hot water. Knock on the tank. If it does not sound hollow, it probably failed, but its possible it just needs to be precharged with air. But if it lost the original precharge in a few years, it must be bad.