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Navien NR-240A – Day 1 Results

December 10, 2011

On Day 1:

My wife took a shower with no issues.

During my shower, I was surprised to get hit by the so-called “cold water sandwich”  — hot water, followed by brief cold water (for about 30-45 seconds), followed by a return to hot water.  The thing is, the circulation unit on the Navien 240A is supposed to prevent this from happening. 

First, here’s what causes the sandwich…  Tankless water heaters have a flow sensor in them so that they can determine how aggressively they need to heat up the water to satisfy the demand.  I’m taking a shower, so it is heating up enough water to keep me happy.  My wife apparently was working in the kitchen sink, which temporarily increased the demand, so the water heater kicked in a few more BTU’s to satisfy both of us.  When my wife turned off the faucet, the Navien over-compensated for the decrease in demand and stopped heating the water altogether, sending me an eye-opening shot of cold water.

To be fair — I have been having some other issus with my Navien 240A (more on that in my next post) so the cold water sandwich could be related to that issue and not a systemic issue.

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From → HVAC

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