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.

 

[Cacher_Chick]

Do you get hot water in the shower if you leave the sink running at the same time?

 

[Sponsor]

 

[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]

Do you get hot water in the shower if you leave the sink running at the same time?

YES, great idea. Not a permanent solution, but the first hot shower I've taken in four days!

 

[Cacher_Chick]

YES, great idea. Not a permanent solution, but the first hot shower I've taken in four days!

That tells me that the heater is not heating the water enough when the flow is low. Navien probably has tech support or troubleshooting information. If there is a flow sensor that is not working properly due to calcium buildup or other defect, that would match the symptoms.

 

[Plumber69]

remove shower head and try. It may be plugged up. Take the water saver out to

 

[JR25]

I have found your issue posted in multiple forums, and have the exact same issue! Please tell me you found the solution!

 

[Delfrancis Dizon]

My NPE-180a does the same thing. Open the sink faucet and get consistent hot water when showering, but give me cold water only when the shower running. I hope you could share if you have fixed yours. Thanks.

 

[Jadnashua]

One thing to keep in mind is that all modern shower valves have some sort of limit on how hot they can get. When it comes to winter incoming water temperatures, if the valve was setup in the summer, it may not be able to turn towards hot far enough. There's nothing wrong with it in that case, but you need to go into the valve and readjust the upper limit so it can get hotter. On a tankless, that will also increase the flow, and if it was marginal before to trigger it to come on, may now make it turn on.

FWIW, on my thermostatically controlled shower valve, to get it over 105-F, you have to press a safety button. A 'regular' anti-scald valve should have been setup to limit the maximum temp to 120, but many people never do, and it's usually set much lower than that at the factory. My summer incoming cold water can be nearly 70-degrees, but I've measured it at 33 in the winter after a cold spell. That will require LOTS more hot for a comfortable shower.

There's an article in the tutorial section that has links to a few brands on how to adjust the hot limit. See if that helps.

 

[Metropoltian]

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.

Possible solution
I have an NPE 240s- I had a similar issue, temp fluctuating and pressure at times also fluctuating, but only sometimes. I replaced the mixing valve (part number 3001 1532a) and the problem solved. Part cost me $75 with shipping and about 15 min to replace, super easy... just make sure you drain the unit.

How we figure that was issue- I called Navien and we looked at the water temp the unit was making and the temp leaving the system. The unit was set to 120, the unit was making water in the 140's but the output was under 100.

 

[Fitter30]

When as the heater cleaned with vinegar?

 

[Simont2022]

When as the heater cleaned with vinegar?

My navien is also doing this to my showers but if I turn faucet on in bathroom my shower works…any idea what is going on

 

[Jadnashua]

First major question for you...when was the last time maintenance was done on it to remove any mineral deposits? Most units require that on at least an annual basis. The heat exchanger can get a significant coating of minerals on it, and the flow sensor can get blocked enough so it doesn't modulate properly.

To heat the water as it passes through the heat exchanger, since it doesn't have much contact time, that must be very hot. That tends to cause any minerals in the water to precipitate out and can bond to that hot surface like what you may see in your tea kettle, if you have one. It's worse on a tankless than on a tank type, but they can get that effect, too over time. That coating on the heat exchanger also acts like an insulator, limiting how much heat can be absorbed by the water as it passes by.