# Tankless WH prob, any ideas/suggestions?



## RealLivePlumber (Jun 22, 2008)

Went to a new customers house today. Referral. She recently remodeled her Master bath. Complaint was that the stall shower faucet temperature wildly fluctuates, scalding hot to cold. It was a Peerless. There is a tee in the shower riser, to a showerhead(above the faucet), and to a handheld(on the opposite wall). Both are on all the time. The handheld volume can be turned down to a trickle at the head. 

I figured it's a POS, so I install a Moen Positemp. I turn it on to set the high limit, and the same problem occurs. Water temp will not stay consistent. I set the limit all the way to hot, and the water temp is around 110 degrees. Back it off a tad, and it gets cold. Fast. Turn the handle to around the 11:00 position (limit a stop at around 2:00), and its lukewarm at best. (Traditionally, this handle position is plenty hot)

I called Moen, they asked if there was a tankless water heater. I look, and there is. A Navien condensing 98. They say pressure balanced faucets don't work well with tankless water heaters. Install a temperature balanced faucet. WTF MF'ers. :furious:

I called Navien, they had me push a bunch of buttons, and give them the numbers off of the LCD. They said the flow rate is consistent, and the outlet temp of the WH is at 120 degrees. Thermistors are ok. (They said that, honest) Must be the faucet. I tell them this is the second one, from a different manufacturer, and it'd only 20 minutes old. They said UUUHHHHHHH, the unit is working fine, and within it's design paramaters. 

I called Moen again. This time, they say I need to adjust the temp of the water heater down. It's at 120 degrees now. We need that for the dishwasher and clothes washing machine, so we can't. The second guy wasn't sure what to say. 

They have other bathrooms in the house. This is the only one with a problem. 

Any ideas?


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## Master Mark (Aug 14, 2009)

*my humble suggestion...*

too bad you did not see that tankless heater before
you got mixed up in that god awful mess... 

I think it might have been
nice of them to mention that to you in the first place....

I suggest you have the guy that installed that tankless
heater in that home to come back and fight with it...
but my guess is they have probably **** canned him over this whole issue already and have gotten you into it knee deep now

I would like to hear the history behind the Navien tankless
heater and why plumber #1 aint around anymore........
.


the double heads in the pressure balanced shower are probably screwing up
the tankless heater somehow,,,,.... 
you already know that and I my guess is that they probably knew it too before you ever stepped foot in the home.........




how about trying a 75 gallon tank type heater, I bet
that will solve the problem??:laughing::laughing:


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## holman23 (Feb 16, 2010)

i wonder if a circulating pump would be affecting you if any installed somewhere that u din't see


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## TheMaster (Jun 12, 2009)

Remove the showerhead and cap or plug that oultet off.....assuming its the closest outlet to the shower valve......and then run the handheld and see if the temp stabilizes......if it does you need to add a positive cut off in the piping to the handheld. Or you could install a thermometer in the hot line near the navien and see if it fluctuates when you run the shower.


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## Protech (Sep 22, 2008)

Put your hand on the tankless outlet pipe. If it stays hot but you are getting temp fluctuations at the shower valve then there is a cross connection in the hot water side somewhere. The number of shower heads does not matter as far as temperature goes, only flow-pressure drop.

Addition: I have installed proly 15-20 moen posi-temp valves on various tankless hot water systems and nver had that problem unless there was a cross connection between the hot and cold systems.


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## TheMaster (Jun 12, 2009)

Protech said:


> Put your hand on the tankless outlet pipe. If it stays hot but you are getting temp fluctuations at the shower valve then there is a cross connection in the hot water side somewhere. The number of shower heads does not matter as far as temperature goes, only flow-pressure drop.
> 
> Addition: I have installed proly 15-20 moen posi-temp valves on various tankless hot water systems and nver had that problem unless there was a cross connection between the hot and cold systems.


Easiest way to check for a cross connection beteen hot and cold is to turn the cold water off to the tankless and see it you sill get flow at a hot faucet thats not pressure balanced


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## aero1 (Feb 13, 2009)

what protech said is the key, just had that experience with a single handle price pfister changed the cartridge and charged the customer parts, labor and head knowledge[thats my favorite charge].


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## Protech (Sep 22, 2008)

good advice :yes:



TheMaster said:


> Easiest way to check for a cross connection beteen hot and cold is to turn the cold water off to the tankless and see it you sill get flow at a hot faucet thats not pressure balanced


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## RealLivePlumber (Jun 22, 2008)

Master Mark said:


> too bad you did not see that tankless heater before
> you got mixed up in that god awful mess...
> 
> I think it might have been
> ...





Protech said:


> Put your hand on the tankless outlet pipe. If it stays hot but you are getting temp fluctuations at the shower valve then there is a cross connection in the hot water side somewhere. The number of shower heads does not matter as far as temperature goes, only flow-pressure drop.
> 
> Addition: I have installed proly 15-20 moen posi-temp valves on various tankless hot water systems and nver had that problem unless there was a cross connection between the hot and cold systems.


 
The original plumber was a no show twice. Customer was a referral, and seems pretty reasonable. 

They remodeled the house, and she wanted copious amounts of hot water. I would have installed a Bradford M2, or better yet, a GX. 

I was laying awake last night, and was thinking cross connection. (The washer is directly below this shower). I guess I'll go back in the next day or two, and have a look around. (There is no recirc) 

Pro, The guy at Navien told me that the numbers on the LCD represent 1)hot water temp leaving the unit, which was 119-120, and 2) flow rate, I don't recall the number. (There was also a couple more values for other ratings). He told me that they have a built in thermistor in the outlet pipe, and that the temp and flow numbers were all good. I hope he ain't bs'ing me.


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## RealLivePlumber (Jun 22, 2008)

TheMaster said:


> Remove the showerhead and cap or plug that oultet off.....assuming its the closest outlet to the shower valve......and then run the handheld and see if the temp stabilizes......if it does you need to add a positive cut off in the piping to the handheld. Or you could install a thermometer in the hot line near the navien and see if it fluctuates when you run the shower.


 I though about that, but if they wanted to use the handheld and the showerhead together, were back to square one. 

Although, it might help to identify the root cause of the problem

Thanks for all the advice, guy's:thumbsup:


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## 1703 (Jul 21, 2009)

Just cuz the reading on the display are saying what they say doesn't mean the thermistor is reading correctly.

Thermistors work on resistance right? (Someone correct me if I'm wrong)

If I'm right, make them give you the ohm values for various different temps and check for closeness in actual reading.

I doubt the thermistors are your problem, but don't let tech support flunkies troubleshoot over the phone- unless you like the runaround.

Good luck.


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## Tankless (Jun 12, 2008)

You answered your own question with that last statement. To me, this doesn't sound like a tankless issue at all. Rarley do tankless units run hot than cold....hot than cold without erroring out or shutting down completely.

It sounds like a bad shower valve in or near the trouble areas. This includes above and below, the troubled areas. 

Protech is correct. Turn something on and put your hand on tyhe HW pipe. It won't lie. If you get consistant hot water you have now proved it is not the tankless unit. Which is hard to believe because it's a Navien POS.

When you were adjusting the Posi, that would make sense to me that you have different responces. Bad cartridges are very sensitive to how thay malfunction with respect to pressures. 

I've seen shower / lavs go hot to cold -- cold to hot just by flushing a toilet.

Thermisters typically don't break, it's just another clue in the puzzle. I would focus on X connection and would be looking at shower valves.





RealLivePlumber said:


> They have other bathrooms in the house. This is the only one with a problem.
> 
> Any ideas?


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## plumr (Jan 16, 2010)

did you every solve the problem


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## robthaplumber (Jan 27, 2010)

Definately check the gpm on the tankless and the gpm on the fixture being affected. I have seen where the gas line was undersized causing fluctuating temps. too. Starving for gas(btu's).


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## Herk (Jun 12, 2008)

There could be a defective Moen cartridge somewhere else in the house causing the problem. I've seen that happen a number of times. Even the newer plastic ones can fail. allowing a cross connection.


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## RealLivePlumber (Jun 22, 2008)

plumr said:


> did you every solve the problem


 No, I haven't been able to get back yet. Our schedules have been conflicting. I hope to get there this week.


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## Tankless (Jun 12, 2008)

RealLivePlumber said:


> No, I haven't been able to get back yet. Our schedules have been conflicting. I hope to get there this week.


If you want to prove what a great plumber you are, pull off the trim and shut off one of the supplies (doesn't matter which one) and then check to see how hot the water gets. Of course this is assuming the shower valve actually has a little 1/4 turn shut off. If not, ya gotta just replace the cartridge. Pulling it out and cleaning it off and reinstalling it may fix the problem, but that's a hack fix and cartridges are usually pretty cheap.


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## RealLivePlumber (Jun 22, 2008)

I don't thinks its a cartridge. It is a brand new Moen faucet. The previous Peerless faucet had the same symptom. 

I am leaning towards the clothes washing machine. It is directly under the problem bathroom. I asked the ho to turn off the control valve(s) to the washer, to eliminate it, but, they said they can't.


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## Redwood (Sep 8, 2008)

RealLivePlumber said:


> I don't thinks its a cartridge. It is a brand new Moen faucet. The previous Peerless faucet had the same symptom.
> 
> I am leaning towards the clothes washing machine. It is directly under the problem bathroom. I asked the ho to turn off the control valve(s) to the washer, to eliminate it, but, they said they can't.


If there are 2 separate valves feeding the washer it's not the problem. The washing machine solenoid valve are pretty much impossible to have cross over...

If they have a Symmons washing machine valve and it will not shut off the water it is very likely the crossover culprit.


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## 907plumber (Mar 13, 2010)

If its a crossover problem why wouldnt it affect the other fixtures?


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## CBP (Feb 5, 2010)

Herk said:


> There could be a defective Moen cartridge somewhere else in the house causing the problem. I've seen that happen a number of times. Even the newer plastic ones can fail. allowing a cross connection.


I think Herk hit it on the head. A bad mixing valve or cartridge near the shower could cause this. I recently had a +/- 40 year old 12 unit apartment building where about half of the faucets wouldn't get hot water. After a couple hours of investigating, I found about 20 older moen cartridges that were bad, allowing cold water to pass through into the hot lines. Rebuilt all of the faucets, and th e place worked good as new!


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