Error Navien 10E 027

Disclaimer: I am not a Navien or HVAC "professional".  I would not perform this type of work if you are not comfortable with DIY projects and have a least a little bit of experience fixing things.  But this does look pretty simple...

I will describe here what might be done to fix Navien Error 10 subcode 27, or Navien 10E 027.

Well the first thing you always try when you have a problem like this is a "reboot". I powered the unit off at the power bar then on again. The error remained. FWIW the error I got looked like this:

image of the Navien control showing error E10 027


Looking this code E10 up in the manual reveals it to be "Abnormal Air Pressure".  So of course the first thing to check is that there isn't any restriction on the air intake - something we've already done on this unit before.  Click here for steps to check and clean the intake air filter.  While the filter is off, if you put your hand close to where the filter lives, you should be able to feel the outside air coming in - which tells you there isn't a blockage in the pipe.  If you can't discern this, then check the intake pipe for any blockages a different way e.g. sight, blow an air hose through...

You should also check that there isn't an obstruction in the exhaust pipe.  I did that by powering off the unit, then powering it on again.  The unit will go through a POST - power on self test,  and if you are outside at the exhaust pipe within a few seconds of cycling the power, you should feel an air discharge from the end of the exhaust pipe.

In my case, I concluded that there wasn't a restriction on the inbound air or the exhaust this time.  Something else was causing the problem. 

I decided to check my Navien warranty to see if my unit was still covered.  The Navien warranty that came with my unit specified that for residential hot water heating usage, the unit was covered for 5 years for everything and 15 years on the heat exchanger from the effective install date.  At this point, my unit is 4 years and 6 months old - so in theory it's currently covered under warranty.

Now before I started calling up Navien or a service person, I decided to look at the diagram for my Navien NR-240A.  Most appliances these days are very simple.  You have a controller board e.g. a computer of some type, and you have some sensors e.g. temperature sensor which plugs into the controller, and you have some motorized devices - which are controlled by the controller after the sensors indicate what action to perform.  Looking at the diagram, I find #25 the Air Pressure Sensor or APS.  Hmmm.  If I'm getting an error that indicates an Air pressure problem, it would seem to me that an Air Pressure Sensor might be a good place to start if we've already verified that there aren't any obstruction in the air intake or exhaust pipes.   I decide to look up E027 in case it's not a subcode, and it actually says:  Abnormal activity of the Air Pressure Sensor.

I traced the wire from the Air Pressure Sensor to the controller board.  With the power of the unit off, I pulled out the APS connector from the controller board.  I then powered on the unit, and... I got the exact same error E10 027.

I went to the Navien website and entered my zip/postal code to find a local Navien Service Provider (Under where it says "NSS Locator"). I called this service provider up and told them about my issue and the code, and also that I'd checked the air and exhaust pipes.  They told me they'd come out to check it - but it would cost me $95 + taxes (minimum - more if it took more than 1/2 hour to diagnose the problem).  I explained it was still under warranty.  They told me it didn't matter - the parts were covered but not the labour.  I asked them if they had an APS in stock.  The replied that they didn't, and that how they did a service call of this type was to diagnose the problem, order the part, and then come back to install it.  And that it would cost me another $95 (minimum) for them to install the part!  What - so that would be a minimum of $230 to fix my Navien that was still under warranty!!! Not a chance...

So I called up Navien Support directly.  They verified the serial number of my unit, and asked a few questions - mostly about air restriction on the intake or exhaust - which I'd already verified.  They said they'd need to send a tech and referred me to the numbers I'd already found for a support company - and they also indicated I'd have to pay for the service calls.

I decided to pull out the APS myself.  I removed the two screws and two hoses (noting the bottom hose was black - "b" for bottom and black), and out it came in about 30 seconds.  I found the part number: KDS-APS-02-D and plugged that into Google. One of the links that came back is the one:  http://www.navienparts.com/Navien-APS-Air-Pressure-Sensor-30000663A-30000663A.htm.  In case it fails in the future, I'll recap here briefly.  The part is available for sale here for $47.81.  It also says the part # is also known as: 30000663A and that it had an old part number: NASS9EX00009 in the past. 

Where to find the Navien APS

 image of the APS removed

 It's not uncommon for part numbers to change when a part is found to be frequently defective.  This also might give a clue that the part fail frequently - so it stands a good chance of being our problem.

Now that I know I have the part number, I can search the world to see the best price option for me.  I find it for just over $40 here:  http://bostonheatingsupply.com/NASS9EX00009.aspx (in case link fails in future, it's listed as $42.31). 

If you are in Canada, these guys carry the part in question:  http://waterheaterspartsdepot.com/index.php?route=product/product&product_id=207&search=663a and once again if the link dies in the future, the listed price is $61.75 CAD.

In my case I decided to order the part and take the gamble.  Besides,  the part could be returned - but with a restocking fee of course.  Even so, the financial risk was pretty low - and they could ship the part out that day and have it to me in 48 hours or less (and it DID arrive in less than 48 hours). 

Once the part arrived, I powered off the unit, undid the 2 screws, gently pulled off the two hoses (already marked).  I then carefully clipped the wireties that tied the APS cord together with the other sensors and  removed it.  I plugged in the new one, put in the two screws, reconnected the hoses, and then re wire-tied the wires together (Note:  take a photo of your box before your start this procedure.  Also make sure you keep wires away from the heat exchanger, and that wires aren't hanging and causing stress - basically make sure you put them back the way they were).

image of Navien Pressure Sensor Connector at the motherboard

The total removal and re-installation time was just under 10 minutes.  It's not a race.  Take your time and pay attention to detail.  I then plugged in the unit and...

It worked!  Hot water once again.  In fact, the water heats up more quickly now AND it's hotter - without changing any settings from what they were before I replaced the APS sensor.  The difference was quite noticable to the extent that if you're having long wait times for your water, or it doesn't seem to get hot enough even though you've jacked the temperature, I'd consider swapping the APS out for a new one (especially if you can return it).

The total cost for this repair including the part, taxes, expedited shipping and my free labour was just under $69 USD.

OK.  So I had to pay for the part even though my unit was under warranty.  I'm fine with that considering it was done more cheaply than 2 service calls, and done faster - who knows how long it would have taken for the contractor to get the part in and schedule an appointment to come and install it, and of course that I'd solved the problem myself.

This issue will go down in my book as being a major problem though.  No part should wear out that quickly under normal wear. 


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