Navien NPE-240A Inaccurate Temperature

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kimmer2k

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I've recently been getting tepid water at my faucet. Navien NPE-240A about 8 years old. I tried cleaning the air filter, water inlet filter, and condenser drain. Descaled for 30 mins. No change. Then I started changing the set temp and recorded the output temp the heater reports vs. the temp at faucets after they stabilize. Here are my results:
set temp (F)output temp (F)faucet temp (F)
110110100
120120110
130130115
140140120

Flow was anywhere from 1gpm - 2.5gpm depending on faucet. Input water temp was around 55F. Faucet temps are ballpark since my thermometer sucks. Even though I don't have "before" temps, temps are noticeably different from what they were before.

No plumbing changes since we moved-in 8 years ago (newly built home). The only thing I can think of is that we had a power outage a few weeks back, but I don't recall if the issue started then or is more recent. We are also getting colder temps outside, but we've been in much colder weather before so that shouldn't matter.

Any ideas on what could be the issue? Thanks in advance!
 
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Bannerman

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If the output temperature is accurate and equal to the temperature setting, then it seems the heat loss is occurring throughout the home's plumbing system. Suggest insulating the pipes where ever possible.

If you are suggesting the output temperature is actually not as hot as the unit is reporting, then it would be best to first establish the variance between the true temp and the reported temp.

Perhaps you may want to invest in a laser thermometer for measuring the outlet and faucet temps.
 

Fitter30

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Used a ir thermometer. Emissivity is the ability of a material to emit infrared energy. Different materials have different emissivity levels which will change accuracy. Electronic thermometer can be strapped to a line and insulated. Basement or ground temp will be lower will effect faucet temperature. The heater is close to in and out settings. Loss is through the pipe.
 

kimmer2k

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Thanks for the replies, somehow they did not hit my inbox hence my late response. I did use an IR thermometer on the output pipe at the unit but it was nowhere in ballpark. For the faucet temp, I used a kitchen thermometer in a cup while running the hot water. I am pretty confident that the unit itself is at fault because the faucet temperature feels much colder than it was before.

Is there a chance that a thermistor on the unit drifted? I'm curious to know if the output temp is the same thermistor used for the control. I found replacement ones on this site: https://www.tanklessparts.com/category/navien-npe-240a-ng-oem-repair-parts but need help narrowing it down. I suppose I could check all of them, but I don't know what resistance they should be at either. Appreciate any help here.
 

GReynolds929

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Switch the two way valve to external, if the temps stabilize the check valve is bad and needs replaced.
 
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