|Vent flue (horizontal) and air intake for tankless water heater.|
Flue enters inside wall of garage and goes straight up to roof.
This piping is now contained in a chase.
Wednesday, January 2, 2013
We are having intermittent problems with our tankless water heater. The system is a Navien NR-180A-NG (operates on natural gas). It was installed in December 2010. The system sometimes fails to deliver hot water. Water will flow, but it's cold. This problem only occurs in the winter.
Examination of the control panel indicates the system is in error mode (red light flashing). I didn't note the error code (will do that next time). The system can be restarted by unplugging it and plugging it back in. This morning it took several tries and about 15 minutes to get the system working.
The service tech examined the system and ran some tests, but when he arrived the system was working and he couldn't duplicate the malfunction. He did set an internal recirculation system (we did not get the external recirculation) so the system is supposed to circulate hot water internally from 0600 to 0900 and from 1800 to 2100. This might improve the time it takes to get hot water to various locations in the house, but it's hard to see how it will help the intermittent problem.
One of the theories for why we're having a problem is buildup of condensate in the flue that exhausts hot air from the Navien. The flue piping has a level section that elbows up (see photo) and water could collect here in the winter, since outside air will be cold and make the pipe cold. If enough water is collecting there, it may be blocking exhaust enough so that the system overheats. We'll have to see what the error code tells us next time the system fails.