Question about Noritz 6.9 Gallon Residential Direct Vent Tankless Water Heater - N

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My Noritz 6.9 flashes a 90 code. I was told by Noritz that this code relates to air flow.. and that the unit needs to be cleaned/serviced. Is this something I can do myself? If so, how do I do it? If not whom should I call?

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I recently started getting an error 90 on my N69-M unit. I finally got a hold of someone at Noritz tech support and they state this error is a general combustion/exhaust/air flow error. Here is what they suggested to look at.
Gas Pressure – The unit has a minimum flow rate for the incoming gas and if the system is gas starved, then you have some sort of obstruction or restriction. If this is a new install and you are getting an error 90, this is likely your problem but if this is an existing install that suddenly started getting this error, unless someone was monkeying around with any values you might have in-line, this probably isn’t your problem.
Air Flow – This is a ventilation issues caused by the build-up of dust, lint, etc that chokes the flow of cool air to the unit and causes the burner to overheat. If your unit runs for a while and then pops an error 90, this is probably your problem. They told me they get a lot of these errors when the unit is installed in close proximity to a clothes dryer, which makes sense. To resolve this, remove the front panel and blow out the intake holes and slots (I tried to shop-vac mine before blowing them out and I was amazed at how much the vacuum didn’t remove). After removing the cover, the first thing you should see is a system board that is covered by a black dust shield. The board is held to the unit by 3 screws (one on the top left and two at the bottom). Remove the screws and let the board dangle by the wires plugged in it. You should now be staring at the fan assembly. They suggested that I either remove the whole unit and clean it out or use compressed air to blow it out. I went with the compressed air route because getting the fan assembly out requires removing and eventually reinstalling 2 relatively small screws way in the back of the unit that you have no real easy way to get to. Blow/clean the fan out and then blow out everything else inside the unit. Reassemble and you are good to go, provided this is your problem.
Exhaust – You might see an error 90 if the exhaust can’t freely flow. Two things can cause an exhaust issue to throw this error. One is that the flapper valve on the outlet of the system sometimes gets stuck closed. This should be easy enough to fix. The other is an obstruction in your exhaust ducting or using too small of a diameter duct to exhaust the unit.
Hope this was somewhat helpful and prevents you from having to wait on hold forever for Noritz support or having to pay someone to fix your problem.

Posted on Jan 22, 2010

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I have a N-084M also shows error code 90. The heater had been used for 3 month then stored for 2 years. The gas is 3/4, about 30ft from the meter. When I mount a loaner, a Rheem 7.4 gpm, it works fine. Tried a Rinnai, it works too. But this Noritz keeps shutting down 5 minutes after the burner starts and displays error 90. I can reset the msg by push on/off on the remote, it will work for another 5 minutes before shut down again. If gas is the problem, I would think the error code should show up winthin 10 seconds. I had the front cover removed, vent disconnected. So air is not an issue here. The problem appears even when the water flow is low (which translate to low on gas useage). I measured the gas pressure at the heater, it's about 10"WC.
But, after move the heater out, mounted on top of the gas meter, it works fine. This has been bothering me for a week. Why this unit demands more gas for the same amount of heat?

Posted on Feb 13, 2010

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Contact Noritz for a certified repair company most plumbers do not know how to repair these I do but you need to have a qualified person in your area

Posted on Nov 15, 2009

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Error Code 90 Solution


Over time after about 5 to 6 years many Noritz heaters tend to display error code 90 and stop working. The unit has to be shut off and back on for it to work again for a short time. Error code 90 is indication of abnormal combustion and can have a few causes, including blockage in the exhaust vent. However the problems lies mostly with the combustion fan. that is the fan that you hear when the unit is running. It is unable to deliver enough air to normal combustion.
Replace the fan and while doing it clean the air pathway with compressed air. In addition remove the ignition and heat senors (all in one assembly, in the middle of the unit) and sand them very slightly with very fine sandpaper (400 or higher) to remove build up on them.
While the fan is being ordered you can at your own risk operate the unit with the cover slightly open (about 2 in.) at the bottom and the unit will run without code 90. It is highly recommended to hire a trained technician for the above work as gas appliances pose a significant danger to human life and property if not installed or maintained properly. This solution is for informational purposes only. Please be safe.
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continuous blinking - typically means ignition failure or the unit is overheating; look for visible water inside the unit, have your gas pressure checked, or check the flame rod/igniter for buildup of debris

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Flashing code 90 .


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1) insufficient BTU supplied to the unit
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3) insufficient makeup air
4) improperly installed exhaust vent

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