Tankless Water Heater not delivering hot water to showers

[James Bojan]

I have a Navien NPE-240A tankless hot water heater delivering hot water throughout the house. All of a sudden, I am only getting luke warm water at each of the showers (which have a single mixing valve for hot and cold). However, I get piping hot water at sinks and the master bath (which all have individual hot and cold faucets).

My first thought was the cartridge in the shower valve was restricting the flow of hot water. I was going to replace the cartridge, but this is happening at all three showers simultaneously.

I had the heater set to 125 deg F outlet, and increased it to 130 deg F with no change in symptoms. The Navien has a flow sensor. When I run a shower at full hot, it's showing a flow around 1.2 gpm of hot water. The hot water outlet is reading around 105 deg F. When I run a single sink faucet at full open, I get around 4 gpm hot water flow, and the outlet temperature is at the set temperature of 125 or 130 deg F.

I cleaned all the water filters in the hot water heater. There was no dirt in any of them. This seems like an issue with the showers, but why would all three cartridges fail at once? I pulled one cartridge out and it looked clean as a whistle.

 

[phishfood]

I have a Navien NPE-240A tankless hot water heater delivering hot water throughout the house. All of a sudden, I am only getting luke warm water at each of the showers (which have a single mixing valve for hot and cold). However, I get piping hot water at sinks and the master bath (which all have individual hot and cold faucets).

My first thought was the cartridge in the shower valve was restricting the flow of hot water. I was going to replace the cartridge, but this is happening at all three showers simultaneously.

I had the heater set to 125 deg F outlet, and increased it to 130 deg F with no change in symptoms. The Navien has a flow sensor. When I run a shower at full hot, it's showing a flow around 1.2 gpm of hot water. The hot water outlet is reading around 105 deg F. When I run a single sink faucet at full open, I get around 4 gpm hot water flow, and the outlet temperature is at the set temperature of 125 or 130 deg F.

I cleaned all the water filters in the hot water heater. There was no dirt in any of them. This seems like an issue with the showers, but why would all three cartridges fail at once? I pulled one cartridge out and it looked clean as a whistle.

The part of your post I highlighted? Have you tried this at just one particular sink, or does this EXACT same thing occur at any sink you have tried?

 

[Geofd]

what brand is you shower valve.....I have run across that in a symmons shower valve you have to change the stem the stock stem works with a hot water tank and there is another that works with a tankless set up see if your shower valve manufacturer makes a different stem or cartridge

 

[James Bojan]

Added info. After cleaning the filters, the unit started dripping water from inside. I opened the panel to see water spraying out of a relief valve on the recirc pump. I shut it all down and cleaned the relief valve. It was very full of calcium buildup. I also pulled some debris out of the pump. Put it all back together and still have the same symptoms. No further leakage from the relief valve. I can't hear the recirc pump running. Should I be able to? Would a faulty recirc pump cause any of this?
Also worth noting is that testing various faucets around the house gives random flow and temperatures. Whenever the flow is high, the temperature is right where it should be. Still seeing higher flow from a single hot faucet than from any shower mixing valve.

 

[James Bojan]

what brand is you shower valve.....I have run across that in a symmons shower valve you have to change the stem the stock stem works with a hot water tank and there is another that works with a tankless set up see if your shower valve manufacturer makes a different stem or cartridge

Delta faucets all around. They have worked fine up till middle of this week.

 

[breplum]

I have Level 3 Navien training.
If your unit is not indicating any fault then investigate the Navien check valve. Pull it out and make sure it is smoothly functioning.
The o-ring can hang up and you may be able temporarily to free it up.
Have Navien send you a replacement. They may not if you are outside of 6 year limit. but they are cheap to buy.
If you have pressure balancing Delta valves, there is a chance that the issue could be inside one of the valves. If the pressure balancing spool is defective, causing a crossover, it can cause crossover mixing.

 

[James Bojan]

More added info. Just took a shower with the hot water faucet running in the sink at the same time. First hot shower I've taken in 4 days.

 

[Geofd]

Delta faucets all around. They have worked fine up till middle of this week.

More added info. Just took a shower with the hot water faucet running in the sink at the same time. First hot shower I've taken in 4 days.

I just re read your 1st post you said "all of a sudden" my theory would be in correct in my case it was immediate breplum is probably onto something

 

[Tnkrst]

I would flush your tankless as well. When was the last time it was serviced?

 

[SHEPLMBR]

Sounds like maybe the flow sensor.

 

[kateaoneal]

I have Level 3 Navien training.
If your unit is not indicating any fault then investigate the Navien check valve. Pull it out and make sure it is smoothly functioning.
The o-ring can hang up and you may be able temporarily to free it up.
Have Navien send you a replacement. They may not if you are outside of 6 year limit. but they are cheap to buy.
If you have pressure balancing Delta valves, there is a chance that the issue could be inside one of the valves. If the pressure balancing spool is defective, causing a crossover, it can cause crossover mixing.

I have a similar issue and would appreciate any feedback. We have a newly installed Navien NPE-240A2. Worked fine until suddenly all showers and sinks stopped running hot water. Only the master bath has hot water consistently. We have to run all of the sinks near the showers to get them to run hot water, sometimes for up to 5 minutes of run-time, and sometimes the hot water only lasts for a few minutes. We flushed the system with vinegar, no change. Navien cust support said call a plumber. How is it that every sink and shower in the house is doing the same thing and the master tub has no issue?

 

[breplum]

If less than a year old, your NPE A2 is full labor and parts warranted. Don't waste your time, call a NSS listed contractor (from Navien's site) and have it done for free (assuming it is installed correctly). No coverage if botched installation.

 

[pmwatts]

This appears to be a common problem (from the internet searching we've done), and I hate to pound it to death, but I'm getting really tired of a sudden cold shower!
We moved into this house in June 2024; house (and Navien NPE-240a tankless heater) are about 5 years old. We doubted that the system had been descaled when we moved in (based on other maintenance not done), so we descaled and cleaned all filters. Hot water was great until about a month ago. Taking a shower with a head full of shampoo (of course) when the water went ice cold. Didn't have hot water anywhere in the house. It was late, so decided to tackle the problem the next morning... when we found that the hot water had come back. Since the first time, it happened again a few times, though we were able to get hot water by turning on faucets elsewhere in the house. We also read a blog that said if you kept a faucet turned on, it kept the hot water flowing to the shower. That did seem to work. After more internet reading, decided it could be the check valve. Purchased a new one about 4 days ago, installed it, and all seemed right with the world. For 2 days. Then the shower started going cold again. So it's been back to leaving a faucet running while we shower.
The only other place this has occurred has been at the kitchen faucet, and that only happened once before we replaced the check valve.
We do not have a dedicated return line in the house for recirculation. The dip-switches are set to external recirculation (1 down, 2 up, 3 down). Nothing has been changed since we bought the house other than the descaling, filter cleaning and new check valve. So,... what do we try next?

 

[havasu]

Are you displaying any faults?

 

[pmwatts]

No, none.....

 

[breplum]

This appears to be a common problem (from the internet searching we've done), and I hate to pound it to death, but I'm getting really tired of a sudden cold shower!
We moved into this house in June 2024; house (and Navien NPE-240a tankless heater) are about 5 years old. We doubted that the system had been descaled when we moved in (based on other maintenance not done), so we descaled and cleaned all filters. Hot water was great until about a month ago. Taking a shower with a head full of shampoo (of course) when the water went ice cold. Didn't have hot water anywhere in the house. It was late, so decided to tackle the problem the next morning... when we found that the hot water had come back. Since the first time, it happened again a few times, though we were able to get hot water by turning on faucets elsewhere in the house. We also read a blog that said if you kept a faucet turned on, it kept the hot water flowing to the shower. That did seem to work. After more internet reading, decided it could be the check valve. Purchased a new one about 4 days ago, installed it, and all seemed right with the world. For 2 days. Then the shower started going cold again. So it's been back to leaving a faucet running while we shower.
The only other place this has occurred has been at the kitchen faucet, and that only happened once before we replaced the check valve.
We do not have a dedicated return line in the house for recirculation. The dip-switches are set to external recirculation (1 down, 2 up, 3 down). Nothing has been changed since we bought the house other than the descaling, filter cleaning and new check valve. So,... what do we try next?

1. why are dip switches set to external circulation? shouldn't be.
2. there is a lot to servicing Navien...customer tech service will not waste their time talking with homeowners, so pro help is what you need.

 

[Twowaxhack]

My experience is Navien tech support is garbage.

They guess at your problem and ship out parts that do not correct the problem. In the mean time you don’t have hot water……..

They had a known factory defect in a heater I worked on but failed to check for that fatal flaw first…..they chose to send out parts even though the parts on the water heater were testing good.

Never again. I won’t even accept service calls on a Navien.

 

[GReynolds929]

Shut the inlet valve at the water heater. Open a faucet to hot only. Water should slow down and stop coming out. If it doesn't you have cold crossover somewhere. What temperature is the heater set to?