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Navien NR-240A – Day 5 Results

December 12, 2011

Well, I didn’t have a chance to keep a journal for how frequently the Navien ran to keep the circulation tank hot, but I do have some good things to report.

  • The water heater worked fine all day
  • No 003 “ignition failure” warnings (none since the tech found and corrected a defect with the unit)
  • No “cold water sandwiches”

On the last bullet, you will recall from my day 1 results that I had experienced this, despite my expectation that the circulation pump/tank would prevent it from happening.   So I ran a little experiment: while taking a shower, I had my wife run hot water in the kitchen sink for 15 seconds.   While I didn’t get a true cold water sandwich, I will say that I got a “warm water sandwich” — not so bad that I had to jump out of the water, but not ideal. 

Here’s what I think happened…  When my wife turned off the kitchen sink, the Navien water heater over-compensated for the decrease in water flow.  Because it has either stopped heating the water or slowed down the rate at which it’s heating the water, I got a shot of water from its circulation tank — which should have been pretty close to 120 degrees (F).  It then realized that there was still demand for hot water and started heating again.   

I think a new standard shower head (I installed this one last year when I remodeled my master bath) has a maximum output of 2.5 GPM, which means it should take 48 seconds to exhaust the 2-gallon tank.  Since the cold water sandwich doesn’t last that long, I’m going to try increasing the temperature on the thermostat to see what happens.  For the record, I have so far kept the Navien set to 120 degrees as preset by the manufacturer and installer.  With three small children (who are all now at the age where they are washing their own hands) I’m hesitant to go much higher, but I think I should be safe at 125 degrees.  If you’re looking for recommended settings, see the US Consumer Product Safety Commision’s article on tap water scalds.

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From → HVAC

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