Feeling stupid, my tankless water heater turns cold when I'm in the shower

[Terry]

Tankless water heaters are fairly new to us, and we're just starting to find out the funny little tricks they play on us. The favorite one is water turning cold while in the shower. That like never happens with a standard vented tank water heater. The tankless is different though. For starters you plug it into electricity to run controls and a fan. With some you get an air intake, often plumbed to the outside and an exhaust, also plumbed to the outside. And don't even tell me you didn't do that one right.

So for those wondering if the water turning cold while in the shower is fixable.............you may want to check the filter on the incoming air. It's a simple little thing to try and does need doing often.

This was performed on a Navien CR-210 from 2009.

Yep.........turning the unit off is a good idea.

OMG, did that dirty filter come out of my tankless water heater? Come on, admit it. You've never, ever even looked at the dirty piece of wire screen in your tankless water heater before.

This filter came from the top left of the tankless.

And now hopefully you will get that warm fuzzy feeling about your tankless while in the shower again.

 

[FinchDaddy]

Thank you, Terry. I'm going to actually check this today before I ask anymore stupid questions.

 

[Sponsor]

 

[Michael Lance]

Hey - I have a Rinnai R75 from 2008, and it did not have a filter! The first time I cleaned the fan, it was solid bug guts. For some reason I thought it was normal for the hot water heater to sound like the space shuttle taking off! I really should have known better. Now I routinely clean it.

 

[MarcinNJ]

I just had a Navien 240S installed to replace another tankless that would rumble loudly and sometime shut off. I began to get cold water sandwiches over and over during a shower after the install. I'd say cold would be gradual descent from hot to warm to cold so we can at least get out of the shower water and ~20 seconds later it goes back up and stays that way for 2-3 minutes then repeats.

I noted the Navien 240S would turn off the flame (at least on the LCD) for ~20 seconds, then fire back up, over and over.

So I get that this is enough evidence to show that if water heater's flame is off then on (and off and on again) during a shower, the exact duration of the fire being off is 1:1 with the duration of cold water in the shower.

Plumber replaced 240S with 240A but even checking the dip switches (#1 on, #5 on) to use internal pump for .5 Gal and well pump (actually a domestic booster we have on the water inlet - city gave us 1.5" instead of 2" so pressure was ~31 and now is closer to ~75psi) are in place.

Same issue - recirculation helps the initial on cold water sandwich, but then recurring ones happen like the 240S so figured the problem is not the tankless but the system:

1. Double checked dip switches #1 and #5 are on, all others off
2. No gas leaks (did the clorox spray - no bubbles, no real smell of gas)
3. Did note that the fresh air intake has a louvered end cap that is for exhaust types (e.g. ,must have pressure from inside PVC to open) so might be some fresh air limit it's reaching - getting contractor to look at this so that variable will be accounted for soon enough).
4. Checked for cross contamination of hot cold and noted my kids sinks do run some cold when hot handle turned on and water heater hot out is off. Retried with their cold water supply off and made no difference but this will also be addressed soon.
5. We have 4 different showers (make/model) and all are affected similarly as our baths. Sometimes even kitchen sink.
6. All plumbing past the water inlet and booster pump and filter is PEX blue/red lines that look correctly connected (dark metal bands cinched on joins) - no leaks noted anywhere in the house.

So other than #3 above, I have no working theories but working with visual confirmation that the flame does turn off (again LCD screen of Navien shows this) every few minutes for about 20 seconds then fires up again. Believe it should be constant.

Looking for any suggestions.

 

[Navien Inc]

I just had a Navien 240S installed to replace another tankless that would rumble loudly and sometime shut off. I began to get cold water sandwiches over and over during a shower after the install. I'd say cold would be gradual descent from hot to warm to cold so we can at least get out of the shower water and ~20 seconds later it goes back up and stays that way for 2-3 minutes then repeats.

I noted the Navien 240S would turn off the flame (at least on the LCD) for ~20 seconds, then fire back up, over and over.

So I get that this is enough evidence to show that if water heater's flame is off then on (and off and on again) during a shower, the exact duration of the fire being off is 1:1 with the duration of cold water in the shower.

Plumber replaced 240S with 240A but even checking the dip switches (#1 on, #5 on) to use internal pump for .5 Gal and well pump (actually a domestic booster we have on the water inlet - city gave us 1.5" instead of 2" so pressure was ~31 and now is closer to ~75psi) are in place.

Same issue - recirculation helps the initial on cold water sandwich, but then recurring ones happen like the 240S so figured the problem is not the tankless but the system:

1. Double checked dip switches #1 and #5 are on, all others off
2. No gas leaks (did the clorox spray - no bubbles, no real smell of gas)
3. Did note that the fresh air intake has a louvered end cap that is for exhaust types (e.g. ,must have pressure from inside PVC to open) so might be some fresh air limit it's reaching - getting contractor to look at this so that variable will be accounted for soon enough).
4. Checked for cross contamination of hot cold and noted my kids sinks do run some cold when hot handle turned on and water heater hot out is off. Retried with their cold water supply off and made no difference but this will also be addressed soon.
5. We have 4 different showers (make/model) and all are affected similarly as our baths. Sometimes even kitchen sink.
6. All plumbing past the water inlet and booster pump and filter is PEX blue/red lines that look correctly connected (dark metal bands cinched on joins) - no leaks noted anywhere in the house.

So other than #3 above, I have no working theories but working with visual confirmation that the flame does turn off (again LCD screen of Navien shows this) every few minutes for about 20 seconds then fires up again. Believe it should be constant.

Looking for any suggestions.

Hi MarcinNJ,

We recommend that you call into our tech support at 1-800-519-8794 option 2 so that we can have our team diagnose the issue and provide a solution. Our tech support is available Mon-Fri from 8am - 9pm EST and Sat-Sun from 8am - 8pm EST. Thanks!

 

[Lifespeed]

Is there a similar screen below the air inlet in my Noritz NRC1111-DV tankless? Will give it a cleaning next time I'm in the attic.

 

[DIYorBust]

Good tip, I have actually had this happen. I really wish the navien's could attempt to restart after an error event. Probably a safety feature, but if we turn off the gas or water pressure and then forget to restart it, that's a cold shower.

 

[Terry H]

I ran into the same problem and it ended up being that the shower head couldn’t deliver the demand of the tankless. It would either be super hot or cold. New shower head with better flow rate stabilized the problem.

Will keep this in mind. Thanks.

 

[DIYorBust]

One thing I will probably do when I get around to it, is put a smart switch on the boiler's outlet. That way I can power cycle the boiler from my phone if necessary.

 

[Bgard]

tankless water heaters do nothing but cost more money to operate and need constant attention and other add ons to allow your washing machine and dish washer to get hot water, big waste of money.

 

[QueBall]

.............you may want to check the filter on the incoming air.

Good one. 1 house back and 7 years back I installed the last generation of Navien tankless in that house. Had some of the usual problems of that gen version, but since I mostly installed it myself I knew I would pretty much always have a good idea what was wrong with it. (Had licensed gasfitter do gas line final assembly and checked my sizing)

So in my case the funny one also was related to air. That plastic grate they gave me in the package fell off the outside pipe and a MOUSE built a nest inside the pipe. Pretty sure the nest was only partially built since at some point the heater likely came on and that mouse decided to move on.

But I had a hell of a time removing the nesting material out of the pipe. Ended up getting furnace cleaning equipment over to have them use their specialized pressurized air tool to push the nesting material back out of the pipe. (Like a plumbers jetting tool but with air instead of pressure washer)
I didn't want to take the pipe apart as I would have had to cut it in multiple spots to get at certain spots and a furnace cleaning company owed me money at the time so we did a deal to waive their late fees if they stopped by to help me.

The included pipe cover was a different plastic than the BH rated flu pipe and the glue I used for the rest of the piping apparently did nothing for the type of plastic the included grate was made from. I got some pvc transition cement to get it to stick the second time. Never really figured if it was PVC or something else but the transition glue got it to bond.


Also every year when the poplar tree seeds float through the air my filter gets so many of those seeds stuck in it I have to clean it all the time. It looks like it is snowing outside the air is so thick with that stuff in the spring.

 

[bradsmithsc]

Hey - I have a Rinnai R75 from 2008, and it did not have a filter! The first time I cleaned the fan, it was solid bug guts. For some reason I thought it was normal for the hot water heater to sound like the space shuttle taking off! I really should have known better. Now I routinely clean it.

Also got a Rinnai tankless water heater. Created this video showing how I go about cleaning the exhaust fan which sometimes can be a bit tricky

Hope that helps