Tips For Buying A Used Inogen One Oxygen Concentrator

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Buying a used inogen oxygen concentrator

Portable oxygen concentrators, which can run up to $3500+, are expensive especially if insurance doesn't cover them.  So if you're paying out of pocket, a used model might be your best option.  But even used models can run from $800 to $2200.  A charger can cost $45 and replacement batteries can cost up to $500.  Because warranties are non-transferrable, it is really important that the used unit and accessories you are buying are in excellent working condition.

When we were shopping for a used oxygen concentrator for a family member, we wanted to make sure we were buying something reliable and that would last for a while.  There are no guarantees when buying a used unit, but a little bit of research can help identify and possibly prevent expensive problems.  Inogen's website says that their oxygen concentrator compressors last up to 25,000 hours, so we knew to check the usage.  The silver sieve beds (metal columns) have an expected life of 1 year before needing replacement, and the batteries were good for 500 full charge/discharge cycles.

One fact quickly became very clear.  Most private sellers didn't know much about the unit they were selling or how to test the unit or accessories.  It doesn't seem unreasonable to want to know more details before making such an expensive purchase.  If the seller has run the diagnostic and oxygen purity tests themselves, ask to have pictures of the status screen results sent to you.  We ended up looking at 3 different units from 3 different sellers and testing them each ourselves.

Here are the list of questions we'd send a buyer before asking to see a unit:

  • What year was the unit manufactured (can be found by calling Inogen customer service with the serial number)
  • How many hours are on the unit
  • Is the unit fully functional, and/or are there any yellow or red indicator lights displayed
  • What is the oxygen purity percentage (can be found by running diagnostic test)
  • Do the batteries hold a full charge

A Word About Batteries

Before visiting a seller, ask that the batteries be fully charged.  Batteries are good for 500 full charge/discharge cycles.  Once they stop holding a charge, you'll have to buy replacements which can cost $294 to $495 for a 16 cell and $195 to $325 for an 8 cell battery.

Testing The Inogen One G3 Oxygen Concentrator

Used Inogen One G3 hours
Checking the usage hours and software version on Inogen One oxygen concentrators

  • Power on the unit.  You will hear the compressor starting up.  It shouldn't be excessively loud and there should be very little (if any) vibration.
  • Make sure the power supply cord has a green light.  If the light is off or flashing, there's a problem with the charger.
  • Look at the status screen on the top of the unit.  It will display the current setting (1 through 4 or 5) and the charge status of the battery.  The status lights should not be yellow or red.
  • Test each of the buttons.
  • Cycle through the settings (1 through 4 or 5)  by pressing the Plus or Minus buttons.  You should hear an increase or decrease in output (depending on the setting).   The unit should not make any unusual sounds or vibrate excessively when changing settings.
  • While the unit is still on, press down on the Alarm (or Mode) for 5 or more seconds until the screen changes.  The unit should now display the hours the unit has been used and the software version that is installed.  Make note of the usage hours.
  • To test the batteries, you have to repeat the following 7 steps in the exact order shown:
    1. Turn the unit off
    2. Unplug the charger from the unit
    3. Remove the battery
    4. Plug the charger back into the unit (do not turn the unit on yet)
    5. Reconnect the battery
    6. Make note of the battery charge level on the status screen.  It should not be blank and it should not show an error message.
    7. Now turn the unit on and remove the charger from the unit.  On some models, the screen will display the charge level as well as time left until needing recharge.  On other models, only the battery charge level is displayed.
  • Remove and inspect the two intake filters on bottom-back of the unit.  They should be clean and no dirt or dust should have accumulated on the inside of the unit behind the filters.   If you do see dirt or residue, then the output filter will probably also need replacement.

If all these basic functionality tests pass, then it's on to the final, most important tests of all: diagnostics and O2 purity testing.  Both these tests are run while the unit is in Autopulse mode.

Diagnostics Test

Inogen one diagnostic tests
Inogen One G3 diagnostic screen

This test will let you know if there are any system problems or parts need replacement, and will help identify any yellow or red blinking lights at the top of the unit.  The manual says that this test should be run for at least 45 minutes.  That's difficult to do when you're at a seller's location.  Fortunately, we've found that most errors or warning messages appear within 5 to 15 minutes of running the diagnostics test.

1.     Start with the Inogen One turned off.  Attach AC power supply and attach nasal cannula.

2.     Press and hold both the Light button for models G2 and G3 (or Plus button for the G4) and the Mode (or Alarm) button simultaneously until the screen displays “Mode Select: Normal”

3.     Press the Plus button once, the screen will display "Mode Select: Autopulse"

4.     Press the Mode  (or Alarm) button once to access the sub-menu, then press the Plus button once – the screen will display “Autopulse: 17 BPM”

5.     Press the Mode (or Alarm) button once and the Inogen One will start up in Autopulse mode

6.     Allow the Inogen One to run in Autopulse for around 45 minutes to run complete diagnostic test.  If there is a problem an error message will appear.

The meaning of all error codes are listed on Inogen's technical manual available online at https://www.inogen.com/pdf/96-03996-00-01-Rev-F_Technical-Manual_Inogen-One-G3.pdf

If the unit has been in use for over a year, it's not uncommon to see the message "O2 Service Soon" which means the silver sieve columns need replacement.  Expect to spend $100 if you replace these yourself.  Messages such as "Service Soon", "Oxygen Error", or "016" could mean that the compressor, concentrator, or motor are going bad. 

O2 Purity Screen

This test is performed while the machine is still in Autopulse mode, immediately following the diagnostics test.

1.     Press and hold the Mode (or Alarm) button.

2.     After 5 seconds the screen will display the clock, software version, and possibly the serial number.  Release the Mode  (or Alarm) button and press and hold the Plus button until the oxygen-purity screen appears, which shows numbers and dashes.

3.     Within about 10 minutes the dashes will be replaced with the oxygen purity percentage, which will fluctuate slightly with each pulse.

4.     Press the Light button to make the O2 purity screen disappear or just turn the unit off.

Anything lower than 82% means that either the silver metal columns will need replacement, or there is an internal leaky valve that needs repair, or worse problems exist.

Used Inogen One Units And Accessory Prices

Here are some average prices from used to new condition to use as reference, which can vary depending on condition and supply/demand.

Carry Bag (CA-300) $48
External Battery Charger (BA-303) $275-$525
Inogen One G3 Backpack (CA-350) $100
Inogen One® G3 single battery (BA-300) $195-$325
Inogen One® G3 double battery (BA-316) $297-$495
Replacement intake particle filters (RP-300) - 4 setting model $20
Replacement intake particle filters (RP-301) - 5 setting model $20
Output Filter Replacement Kit (RP-107) $20
Inogen One® G3 columns (RP-320) - 4 setting model $99    
Inogen One® G3 columns (RP-321) - 5 setting model $99
DC Power Cord (car charger) $65

Oxygen nasal cannula (25ft min) $3
Oxygen tubing (25ft min) $3.50
Oxygen mask $8.00

A new Inogen One G3 with one single battery, AC/DC power cords and carry bag sells for $2300.  Add additional accessories and the prices increase.  Like with almost everything else used, you should expect to pay 35-60% of that price for a used unit in like-new condition from a private seller.

What To Do If Your Portable Oxygen Concentrator Needs Repair

If you purchased a used unit that ends up having a problem, or your existing unit is no longer under warranty, you still have a few options on getting it repaired.  And if it's under 15,000 to 20,000 hours, it may be worth the investment and expense of repair.  You can check online for oxygen concentrator repair centers.  On average, expect to pay about $75 an hour.  You can also buy a 90 day warranty directly from Inogen for $229 which will cover repair costs.  The customer care agent we spoke to said that the unit can be sent to their repair center in Texas after purchasing the warranty, but to expect 8-10 weeks for it to be returned.