Navien NPE-240S2 pressure relief valve

[petrichor]

This might be a stupid question, but just wanted to ask in case I did something really bad.

My Navien was installed last year, and I was doing a maintenance for the first time. Everything was going well until the very end. After running vinegar through the unit for 45 minutes, I opened the pressure relief valve to drain the vinegar out of the unit, but forgot to close it back. I opened the water inlet valve and flushed for five minutes, as per the manual.

After disconnecting the hoses and closing the service ports, I opened both the inlet and outlet valves to fill the tank. When it did not stop filling, I realized that the pressure relief valve was still open. When I closed it, the heater stopped filling immediately and made a "thunk" noise. I am guessing that I should have closed the inlet valve before closing the pressure relief valve. The heater booted up afterward and seems to be running normally, but I am wondering if closing the pressure relief valve like this would have caused any damage.

 

[John Gayewski]

Your fine. That clunck was water hammer. If it did damage it would, in all likley hood, be evident immediately.

 

[Sponsor]

 

[petrichor]

@John Gayewski Thank you for your insight. I read up on water hammer and now have a better understanding of the physics involved. I will take more care in the future.

Given that I "flipped" the switch fairly quickly, it seems that the pressure spike could have potential been in the 500-1000 PSI range. If damage were to have occurred, would it be inside the heater, or would it be the pipes? In case it matters, there should have been some air in the hot outlet pipe because the faucets were drained before maintenance. Would this have provided some cushion?

 

[John Gayewski]

@John Gayewski Thank you for your insight. I read up on water hammer and now have a better understanding of the physics involved. I will take more care in the future.

Given that I "flipped" the switch fairly quickly, it seems that the pressure spike could have potential been in the 500-1000 PSI range. If damage were to have occurred, would it be inside the heater, or would it be the pipes? In case it matters, there should have been some air in the hot outlet pipe because the faucets were drained before maintenance. Would this have provided some cushion?

Yes air provides cushion. Like I said if your broke something it would leak. Water hammer happens all of the time and while it's not good and can cause issues, most of the time it doesn't break anything. Bigger pipes causes more of an issue that smaller pipes.