Condensation problem with old tankless heater AND with replacement

[Ed Boston]

Hello, I previously had a Navien 240A for about ten years, not many issues with it. Several weeks ago it started spitting out condensate from the exhaust vent and dripping water from the T&P pipe. Nothing about the installation has changed, same intake and exhaust pipes which are up to code and pitched back toward the unit. Plumber opened up the unit and it was covered with condensate inside. Given age of unit and not much help from Navien tech support I decided to replace with a new Rinnai RXP160. Installed with no problem on the existing intake/exhaust setup and worked fine for a few weeks.

Now it's also dripping a bit of condensate from the outside exhaust vent and from the T&P. It is still heating correctly otherwise. Haven't opened the unit since it's a new install, setting up a service call for next week.

What could cause this? I asked for advice on the previous problem in a different forum and was advised to look at the exhaust pipe pitch, which seems to be fine and is solidly anchored in place. Could this be caused by intake and exhaust vents being too close together, which is the only thing I can think of? Greatly appreciate your help as this is driving me crazy now.

 

[Fitter30]

All condensing water heaters run water that's how they get there efficiency. Page 26. 4.5.2. #6. Slope back to heater 1/4" to a ft

https://media.rinnai.us/salsify_asset/s-5dcde422-3307-426c-ab15-29ecd56cac15/100000839%20SENSEI%20RX%20Residential%20Installation%20and%20Operation%20Manual.pdf?_gl=1*1g4x1j*_gcl_au*MTMyOTMyNTIxLjE3MjcxMDY3MDk.*_ga*NTkyODQ2NTEwLjE3MjcxMDY3MTA.*_ga_K9LQBM5WS9*MTcyODA2OTYzNS4yLjAuMTcyODA2OTYzNS42MC4wLjA.&_ga=2.240473606.461440143.1728069636-592846510.1727106710

 

[Sponsor]

 

[Ed Boston]

All condensing water heaters run water that's how they get there efficiency. Page 26. 4.5.2. #6. Slope back to heater 1/4" to a ft

https://media.rinnai.us/salsify_asset/s-5dcde422-3307-426c-ab15-29ecd56cac15/100000839%20SENSEI%20RX%20Residential%20Installation%20and%20Operation%20Manual.pdf?_gl=1*1g4x1j*_gcl_au*MTMyOTMyNTIxLjE3MjcxMDY3MDk.*_ga*NTkyODQ2NTEwLjE3MjcxMDY3MTA.*_ga_K9LQBM5WS9*MTcyODA2OTYzNS4yLjAuMTcyODA2OTYzNS42MC4wLjA.&_ga=2.240473606.461440143.1728069636-592846510.1727106710

Thanks very much for the reply. Yes, as I mentioned the exhaust was installed with the correct slope. It has functioned fine for years and now it is dripping from the exhaust and the unit. I replaced the unit and the new unit is also dripping.

 

[Fitter30]

Thanks very much for the reply. Yes, as I mentioned the exhaust was installed with the correct slope. It has functioned fine for years and now it is dripping from the exhaust and the unit. I replaced the unit and the new unit is also dripping.

Dripping from exhaust out the end, flue joints top of unit, bottom of unit? Take a few pics.

 

[Ed Boston]

Dripping from exhaust out the end, flue joints top of unit, bottom of unit? Take a few pics.

Thanks for bearing with me. It’s dripping from the exhaust out the end and also from what I think you’d call the T&P valve drain. I don’t see any other dripping around the unit. Dripping is slow and intermittent, mainly happens after the unit has been used for a while like somebody showers and then dries up under light use.

Haven’t opened it up since it’s a brand new install. I took some pics with my phone but the site is telling me they’re too large. I’ll try to reduce them on computer later if I can.

 

[Ed Boston]

Dripping from exhaust out the end, flue joints top of unit, bottom of unit? Take a few pics.

OK here are pics. One of condensate dripping out the exhaust vent, the other of dripping from the T&P drain. Sometimes it's more than this, this is a fairly small amount.

 

[Fitter30]

T&P valve dripping is there a expansion tank on the cold water line by the heater? Need a gauge to connect cold water line t&p valve is set 150 lbs or 210°.

Amazon.com

 

[Ed Boston]

T&P valve dripping is there a expansion tank on the cold water line by the heater? Need a gauge to connect cold water line t&p valve is set 150 lbs or 210°.

Amazon.com

Ok thank you, I know we don’t have an expansion tank so I will bring it up with the plumber.

 

[Ed Boston]

T&P valve dripping is there a expansion tank on the cold water line by the heater? Need a gauge to connect cold water line t&p valve is set 150 lbs or 210°.

Amazon.com

Ok thank you, I know we don’t have an expansion tank so I will bring it up with the plumber.

 

[GReynolds929]

Picture of the tankless, venting, and piping would help.

 

[John Gayewski]

Do you have a recirc line?

 

[Ed Boston]

Picture of the tankless, venting, and piping would help.

Sure thing, working a long weekend shift but will get some when I get back home.

 

[Ed Boston]

Do you have a recirc line?

No, no recirc line.

 

[Ed Boston]

Picture of the tankless, venting, and piping would help.

Here they are, thanks for bearing with me.

To restate the problem: intermittently seeing condensate spurting out the exhaust vent, and dripping from the T&P drain. Here are pictures of the unit, piping, and intake/exhaust runs.

 

[John Gayewski]

Do you change your condensate neutralizer? I would check the condensate drain and neutralizer for flow blockages even if it's not blocked and just slowed that could you exhaust to spit water.

Your t&p issue is seperate. I assume the t&p is new with the new heater?

 

[Ed Boston]

Do you change your condensate neutralizer? I would check the condensate drain and neutralizer for flow blockages even if it's not blocked and just slowed that could you exhaust to spit water.

Your t&p issue is seperate. I assume the t&p is new with the new heater?

Thanks for the reply! Here is what's going on with each issue:

1) Condensate: the condensate drain is air-gapped from the unit and there's no visible overflow at the gap so I think that rules out a neutralizer/drain/pump problem. Exhaust pitch is overall sloped towards the unit but the final 8-12" are relatively flat. Maybe a partial blockage somewhere in the exhaust that is causing water to pool and then be spurted out intermittently?
2) Yes, T&P is new with the new unit.

 

[John Gayewski]

Thanks for the reply! Here is what's going on with each issue:

1) Condensate: the condensate drain is air-gapped from the unit and there's no visible overflow at the gap so I think that rules out a neutralizer/drain/pump problem. Exhaust pitch is overall sloped towards the unit but the final 8-12" are relatively flat. Maybe a partial blockage somewhere in the exhaust that is causing water to pool and then be spurted out intermittently?
2) Yes, T&P is new with the new unit.

The spitting. I think is fine. It could be slowly accumulating in a flat spot and then being ejected as would be normalish.

The t&p should only eject if the water pressure exceeds 150psi. I think those units should have a pressure sensor and give off an error code in the case of high pressure. Can you look through the units display and find any history of pressure issues or a current pressure status?

 

[Ed Boston]

The spitting. I think is fine. It could be slowly accumulating in a flat spot and then being ejected as would be normalish.

The t&p should only eject if the water pressure exceeds 150psi. I think those units should have a pressure sensor and give off an error code in the case of high pressure. Can you look through the units display and find any history of pressure issues or a current pressure status?

OK, thank you. I'll get back to you on the error codes.

 

[GReynolds929]

What's the water pressure measure at the unit? You can put a gauge on the cold inlet service port and open it to measure, or use a hose bib on the house? You most likely need an expansion tank, and maybe a PRV if pressure is high enough.

 

[Ed Boston]

What's the water pressure measure at the unit? You can put a gauge on the cold inlet service port and open it to measure, or use a hose bib on the house? You most likely need an expansion tank, and maybe a PRV if pressure is high enough.

That I am not equipped to do myself right now but I appreciate the suggestion and will ask the plumber. We do have pretty high water pressure in the house according to plumbers I’ve worked with in the past.