Tankless conundrum leaving us with chilly showers

[mptrauber]

Hello everyone,

I'm two days into having a Noritz NR71 installed and am getting some odd results.

I'm hoping some of you guys can point me in a good direction.

Here are the symptoms:

1) Turn on hot valve at the lav in bathroom alone, unit comes on and stays on: hot water as expected
2) Turn on hot water at tub/shower in same bathroom alone (full), unit comes on for 15 to 30 seconds, then shuts down: NO hot water
3) Turn on clothes washer with hot or warm setting alone, hot water as expected
4) Turn on warm setting washer and tub/shower at the same time, unit comes on and stays on providing hot to both until washer stops filling, then shuts down with no hot water to tub.

Possibly pertinent additional info:

1) Plumbing had to be repaired above this bath after old HWH was removed and before new tankless was installed. There is a possibility that hot and cold were crossed at the tub.
2) Bath valve is single handle that rotates 90 deg left only.

Noritz people came up with the theory that it was a gas pressure problem; that the extra demand of the tub over the lav was too much flow for the amount of gas coming in, but the clothes washer and tub working together seems to defeat that idea.

Noritz also thought that some installation debris might be blocking the incoming cold water, but the increased demand of two appliances running seeming to make it work also seems to defeat that idea.

Thanks very much in advance for any ideas.

Mike in Texas

 

[Thatguy]

1) Turn on hot valve at the lav in bathroom alone, unit comes on and stays on: hot water as expected
>At the 2 GPM rate determined by the aerator, I assume.

2) Turn on hot water at tub/shower in same bathroom alone (full), unit comes on for 15 to 30 seconds, then shuts down: NO hot water
>If it starts back up after a few seconds it works just like every tankless heater in Germany that I used.

3) Turn on clothes washer with hot or warm setting alone, hot water as expected
>At what GPM (your water meter and a clock will tell you)?

4) Turn on warm setting washer and tub/shower at the same time, unit comes on and stays on providing hot to both until washer stops filling, then shuts down with no hot water to tub.
>It seems to be responding to a decrease in demand. Check your GPM demand [see #3] for each appliance that you have used, but this does seem to contradict #1's response.

1) Plumbing had to be repaired above this bath after old HWH was removed and before new tankless was installed. There is a possibility that hot and cold were crossed at the tub.
>How can you confirm/disprove this?

I wonder if the thing is responding to the rapid change in GPM that you get when the washing machine valve closes.

Also, with a clock and your gas meter you can check that this thing is consuming gas at the design rate.

You could ask Noritz for an e-mail confirming that there is no Noritz Technical Service Bulletin that addresses this problem.
What Noritz says needs to be in writing. If you e-mail them and they respond by calling you, watch out.

There are a lot of analogies between electrical circuits and plumbing 'circuits.' For an electrical problem analogous to your problem I'd use recording voltmeters, recording ammeters and oscilloscopes. I don't know if plumbers have the plumbing equivalent of these instruments.
Ask Noritz what they would use to troubleshoot this problem. As always, the countermove to the "I don't know" answer is, "I respectfully request that you immediately refer this complaint to someone who does know."

A tanked heater dumps a few kw into 50 gals of water and takes a half hour to do it.
These tankless things dump a large amount of power into very few gallons of water and they have to respond instantly. IMO these heaters are treading a thin line between adequate performance, inadequate performance and catastrophe.
Lawsuits make for bad press so the choice is between the first two. Not many people sue over a cold shower or touchy, flaky performance.

 

[Sponsor]

 

[hj]

Gas heaters do not dump "kws into the water". Initially, it looks like a gpm problem, although the washer and shower together getting hot water, but not when the washer turns off, is counterintuitive to that. What happens when you select "hot" water, not warm, at the tub while the washer is filling with "hot" water?

 

[mptrauber]

I think I figured it out

Gas heaters do not dump "kws into the water". Initially, it looks like a gpm problem, although the washer and shower together getting hot water, but not when the washer turns off, is counterintuitive to that. What happens when you select "hot" water, not warm, at the tub while the washer is filling with "hot" water?

Even though there's a lot of water coming out of the tub faucet, the mixing valve is set to add the hot in the last 15 degree of the ~100 degree sweep of the handle. So, it's actually not as much as the lav by itself unless added to by the lav or washing machine.

So, I crank it for full heat and once flow is consistent, I can back it off.

As obvious as this is now to see, it was kicking my tiny mind. I really appreciate folks reading my post and helping me out.

 

[Thatguy]

Gas heaters do not dump "kws into the water".

My bad. To be really generic I should have said kilojoules per second of power.