Another Navien Repair

I'll say this for the standard hot water heater -- the kind with a tank -- it doesn't have a lot of moving parts and it certainly doesn't have a lot of electronics. The same can't be said for the typical tankless hot water heater. Just look at the Navien.

Navien NR-180A Tankless Hot Water Heater

The more stuff you cram into these 17" x 28" x 14" boxes, the more can go wrong. We've had problems with our system ever since it was installed in December 2010. The last fix was replacement of the flame rod assembly. Before that, we had to cut into the wall and pull the exhaust pipe down to create an incline for the condensate to drain properly.

This time around the problem was the air pressure sensor (APS). The new APS Pt# was 30000663A, and replacing it also required replacing the whole damned printed circuit board (PCB), Pt# 30000182A.

The APS is located at the top, right side of the unit.

This job went fast, less than an hour, once the problem was diagnosed, and it took time on the phone with Navien tech support to figure out what was wrong. We had, at different times, error codes 3, 10, and 12; ignition failure, abnormal air pressure, and flame loss. None of these codes made reference to the APS or the PCB.

Studying the Navien Problem

As indicated in an earlier blog post, we have had problems with our Navien NR-180A-NG tankless hot water system each winter since its installation. The system fails to ignite (Error Code E003), and thus won't deliver hot water. This happens only during winter weather, i.e., when it's very cold outside. The last time it happened was in January 2013. The error code displayed then was E027, "Abnormal activity of the air pressure sensor."

One of the theories for why we're experiencing this problem is buildup of condensate in the flue that exhausts hot air from the Navien. The flue piping has a long 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 senses an air pressure problem. We've been able to reboot (unplug and plug) the system and get it working again.

Matt and Chris Q of Campbell & Company were out today to examine the system and discuss what might be done to correct the problem. It was generally agreed that the long run of the vent pipe and failure to slope the pipe the designated amount (1/4" per foot) is the major contributing factor in the system failures during cold weather. However, Matt hypothesized that another factor may be the fact that the cold air in the winter is harder to move through the long exhaust pipe. The combination of the condensate building up in the pipe and the added difficulty of moving the heavier cold air may be causing the air pressure anomaly and failure to ignite.

We hesitate to go in and realign the exhaust pipe because it is housed in a chase for cosmetic reasons (see photo below).

Matt disconnected the intake pipe on the Navien so that warm air is being drawn from inside the home (see photo below), rather than outside. We'll see if this fixes the problem when the weather turns cold. If not, we'll have to cut a hole in the chase where the vent pipe is located and attempt to incline the pipe and exhaust it directly under the deck instead of on the roof.