Might my Noritz tankless be misreading the flow rate?

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Fitter30

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Flow control is read by a magnetic sensor item 412
411 is the complete sensor
 

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Reach4

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it appears to use an impeller for sensing flow.
Hard water deposits on a turbine blade could cause low-reading, I would think.

Is there a symptom other than the measuring discrepancy? I would think that symptom might be to require more flow to start the WH. You might have said that, and I missed it.
 

Nathan Meyers

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Hard water deposits on a turbine blade could cause low-reading, I would think.

Is there a symptom other than the measuring discrepancy? I would think that symptom might be to require more flow to start the WH. You might have said that, and I missed it.
Thanks for responding, Reach4.

The water is softened, so deposits are unlikely. I don't know if burner trigger points have changed - this is something I haven't paid attention to until recently. Hot showers were fine for 1-1/2 years, until about a month ago. That's when we returned from a vacation during which the water supply was turned off. Coincidence? Tech says the WH will not be affected. I've cleaned and descaled the Speakman showerhead, which did not help. The discrepancies are strange, and appear to put our showers much closer to the trigger point than they really should be.
 
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Nathan Meyers

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Here's the latest in the saga of my tankless cold showers...

I have measured much more carefully, using a gallon bucket, and confirmed that the unit is consistently reporting flow rate about 30% low, leading to unfortunate heating decisions. The plumbing tech's response in a revisit is: it's not a precision instrument.

30% error couldn't possibly be within tolerance, could it? Am I being unreasonable to expect heating at .95 gal/minute? The good news is that the plumbing tech is arranging for me to talk to the area Noritz rep, so maybe we'll make some progress.
 

Fitter30

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Would think 30% is way off. The magnetic flow meter technology has been around for 20 years at least. If it takes 64 oz / .5 gpm to make flow switch 30% difference 83.2 oz. The difference in the flow switch should only be a problem at low flow after switch is made temp sensor should take over.
 

Nathan Meyers

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Would think 30% is way off.
Yes. The tech has been giving me excuses like "it's not a precision instrument" and "all parts have tolerances" and "inlet temp is higher in the summer", but 30% off is just way too far out of spec. Needing to pull 1 gpm to trigger the burner is way too far out of spec. Is it extremely difficult to engage Noritz in these issues? Is that why the tech is trying to convince me this is not the heater's problem?

Yes, he went through a phone call with Noritz and reported some values from diagnostic mode, The tests passed, but it's obvious they do not measure the accuracy of the flow reading. I can show the problem clearly with a bucket and a stopwatch, but apparently that counts for very little. I don't like being a screaming obnoxious customer, but things are heading in that direction.
 

John Gayewski

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Yes. The tech has been giving me excuses like "it's not a precision instrument" and "all parts have tolerances" and "inlet temp is higher in the summer", but 30% off is just way too far out of spec. Needing to pull 1 gpm to trigger the burner is way too far out of spec. Is it extremely difficult to engage Noritz in these issues? Is that why the tech is trying to convince me this is not the heater's problem?

Yes, he went through a phone call with Noritz and reported some values from diagnostic mode, The tests passed, but it's obvious they do not measure the accuracy of the flow reading. I can show the problem clearly with a bucket and a stopwatch, but apparently that counts for very little. I don't like being a screaming obnoxious customer, but things are heading in that direction.
Bottom line, itsy not performing as advertised you should get what you payed for.
 

Nathan Meyers

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It turns out Noritz is much more end-user friendly than I expected. A new flow meter is on the way. They tell me I can even DIY replacing it, which I would do if I could get the cover off. Seems I need to have a conversation with my contractor about their use of an impact driver to tighten the cover screws after the last flush. Ugh... it's been a long couple of weeks.
 
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