Navien ncb 210E. Heat pressure keeps rising

Bill934

I installed this boiler about 2 1/2 years ago and yesterday the customer called me went over there. The pressure was 29.8 blowing out of the pressure relief valve. Release the pressure I even turned off the incoming water and the pressure keeps rising. Called Navien tech they are not really sure.
I will be calling them again this morning. They are getting heat and they are getting hot water. However, the pressure keeps rising. I did install the expansion tank on the return side however, I might be starting on the feed side. Also question, what is the psi of the expansion tank supposed to be in these Naviens?

nick31

If it’s a combi boiler try shutting off the cold water inlet at the boiler. I’ve had a boiler that was feeding water from the inlet of the domestic side to the boiler side. This wasn’t through an auto feeder or through Navien’s 1/2” tapping for feeding water. This was at the flush valve of the domestic water. Unfortunately I cannot tell you exactly how it happened or how I fixed it. The customer was standing over my shoulder and as soon and me turning the domestic water off stopped the rise in pressure on the boiler side he told me to stop everything and that he was going to have his plumber who installed it come out. I’m an hvac tech who works on boilers. The whole situation was weird. The floor of this closet the boiler was in had a graveyard of igniters, 007 pumps, a 3 way valve and a flat plate heat exchanger to tbh I didn’t mind leaving someone else’s mess. My guess is when they changed the 3 way valve or flat plate heat exchanger they messed something up. 

pedmec

Sounds pretty obvious that the water side heat exchanger has failed.

Bill Julian

Interesting you guys say this because yesterday I tried to run vinager through the Heat exchanger DHW and the water would not come through (very weird). Ive cleaned many or these with no problem. Nothing coming out. Utility pump fine etc.
I called Navien he walked me through some things but no real answer. I tell all my customers to call me for cleaning every year. She waited 19 months. Still not sure of the problem will call Navien again this morning.

Keep in mind there is plenty of heat and hot water so if the Exchanger has failed why the hot water and no leaks? Will check in later for replies, thanks !

GGross

turn off the boiler, close the fill valve, close the cold domestic water valve on the combi, let off pressure until you are where you need to be for the system. Boiler should be relatively cold at that point, observe the pressure gauge. If the pressure does not rise here, open the cold domestic valve on the combi side, observe the pressure again. If it rises at this point I would say the flat plate for DHW is leaking into the boiler, if not, close the cold inlet again, confirm that the fill valve is set to the pressure your system is set at, now open the fill valve. If the pressure rises with fill valve open above the pressure setting you probably need new fill valve. If the pressure is rising with boiler off, fill valve closed, and domestic cold closed, one of your valves is leaking by. If pressure does not rise under any of these circumstances, with the domestic side closed, and the fill valve closed let the boiler start up to run a heat cycle, if the pressure rises over an acceptable amount at that point look at the heating system expansion tank, confirm it is set to system pressure.

there is no manufacturer specific PSI setting for an expansion tank. You set the expansion tank pressure to match the system, you set the system pressure to meet the system requirements (between 12-18 PSI depending on how many floors)

Bill934

Thank you for all of that. Took all that time. Thank you.

I spoke to Navien tech-support this morning he walked me through everything with the domestic cold shut Pressure does not rise. We determine that it was the domestic heat exchanger. He’s sending one out

But here’s what I can understand and he could not understand when I try to clean the domestic heat exchanger the water would go in, but it would not come out the other end. Very very strange. I’ve cleaned many of these.
Yeah, there’s no leaking internally inside the Navien there’s heat there’s hot water.
I cannot understand why, as I always use, will not purge through the domestic cleaning valves

GGross

depending on how the heat exchanger was compromised I imagine it could show the issue in some strange ways, I would expect that if you couldn't purge they wouldn't have hot water either but sometimes these things are a bit more complex than I can see at face value. Please update us once the new DHW heat exchanger is installed.

Bill934

I will update fur sure. The HE to be overnighted
from navien. Thanks for your time!

Bill934

GGROSS

I think I might know the reason why I was unable to de-scale, using my service valve on the Navien. A possible reason is that the compromised tankless exchanger sending the descaling solution into the cold side on the domestic must’ve been blocked by the pressure of the heat side boiler water infiltration And I don’t know how much pressure my 1/4 hp Wayne pump produces, but apparently not enough to get through the tankless exchanger and out the other side into my bucket. When sending Street pressure through the HE domestic cold side and out the domestic hot side service port I have no problem doing that. And today I will receive my new Navien heat exchanger and install, will update.

Bill Julian

I noticed in the UK some guys use acid to flush heat exchanger. Not too sure that's a good idea. I have been using vinegar for years seems to be fine. However this customer did not clean for 19 months and the HE is now compromised. I believe the heating side should also be power flushed might start doing that too as part of the service.

GGross

Flushing with Vinegar is a good regular maintenance, or another descaling solution. You can also fully remove them when doing annual service and soak in a cleaning solution while you do the other annual maintenance items. I never see contractors do this in the US, but have seen it done as a standard from several companies in Europe

Bill Julian

The DHW exchanger was installed today a beast of a time installing. Disconnecting various components and reinstalling them this time around were difficult. The hot side brass 90-to- exchanger gave me fits. The small screws that secure the water to the jacket so difficult to reach with screw driver. Navien should change this design. Make it more assessable and easier to replace as needed.
The rubber orings leaked 3 or 4 times upon install b/c if they are not seated properly in the slightest location, they leak. Poor design by Navien makes me want to change manufacturers. Rinnai a nice machine, Bosch, and others.
Going back tomorrow and see if things are holding. Beastly job. The Exchanger was leaking into the heat side. The pressure is now holding at 17-20PSI. We will have a look in the morning to confirm. Thanks for your input.

Bill934

I have another Navien combi where the pressure is rising to 27.7 LBS. No discharge for TP but the pressure should not be that high. I released the pressure but is rises anyway but never gets higher then that. I see no cross connection to the heat and DHW the boiler is only 10 months installed.
I am. It using an auto feeder I’m using the Navien auto feeder. Any thoughts?

pedmec

Is 27 the static fill psi or does it rise when heated?

Bill Julian

Rises when heated

pedmec

then it sounds like your expansion tank might be undersized or shot. does the pressure recede when the water cools down?

Bill Julian

I'm not at the job. The water likely never cools whereas the DHW and Heat side in near constant use. I need to check pressure on Extrol tank. Homeowner added a heat zone in his basement (didn't tell me). I went over and purged the zones baby sat it and noticed the pressure rising to 27.4. Bled off some pressure sat around a spell pressure stabilized to about 19PSI left the job and 3 hours later he texted me the rise in pressure to 27.

Its been 27 psi for months I installed this combi Jan 2022. Never rose possibly until he added the zone. It also never blew the t&P. You might be right the extrol tank.

Bill Julian

Extrol is 19PSI I took it down to 13 PSI the pressure in the boiler is now 21.6 I can live with that