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.