During the 1st heating season my Navien operated at a pressure reading of 21.8 during a call for heat. manual shows an operating pressure between 7 and 30 psi. After I drained the unit (Oct 30, 2014)before the 2nd heating season to clean. the unit operated at the same pressure as the last season. Over the course of the next 2 months the pressure slowly went down, ended up with a reading of 14.2 while producing heat. I checked the crawl space and found no leaks when the circulating pumps were running. During the last week the pressure went up to 16.7 when running. The manual says that the auto feed will only add water when pressure is lower than 7.4 The Navien seems to be operating normal except for the reading on the pressure gauge. Do you have any ideas what would cause it to run at a lower pressure this heating season. I have hot water baseboard. Appreciate your help
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