My air quality monitor shows high CO2 levels even with the windows open
Home Nura guide — category: Air Quality Monitors
Diagnosis
This symptom is common and usually harmless. Most of the time, a targeted cleaning or a small change in how you use the device fixes it in under 10 minutes.
What to do
Unplug the device, let it cool down, then clean the affected part with warm water and mild dish soap (never an abrasive scrubber on nonstick coatings). Put it back together, plug it in and run a short empty cycle to make sure it works.
Repair or replace?
If the problem is still there after these checks and the appliance is out of warranty, weigh the repair estimate against the cost of a new model.
If you're replacing it
Air Quality Monitors: the picks from our buying guide
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Best overall
Airthings View Plus
It combines radon, PM1, PM2.5, CO2, VOCs, humidity, temperature and pressure, and runs on batteries or plugged in: the most complete pick here.
Photo: © Airthings
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Best value
Netatmo Smart Indoor Air Quality Monitor
It tracks CO2, humidity, temperature and noise over Wi-Fi, with no subscription and Apple HomeKit support, so you know exactly when to open a window.
Photo: © Netatmo
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Best for reliable, portable CO2
Aranet4 Home
Its NDIR sensor and battery-powered e-ink screen show CO2 at a glance for years, and it moves easily from room to room.
Photo: © Aranet
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Other common problems in this category
These issues affect the same type of appliance — each one comes with a diagnosis and the steps to take.
- Air Quality MonitorsMy air quality monitor gives inconsistent readings
- Air Quality MonitorsThe batteries in my air quality monitor die within two weeks
- Air Quality MonitorsHow do I set the alert thresholds on my air quality monitor?
- Air Quality MonitorsThe history on my smart air quality monitor has gaps in the data
Frequently asked questions
Check the manufacturer's warranty first: how long it lasts and what it covers vary by brand and model, so read the terms for yours and keep your proof of purchase. If you bought it new in the EU, a two-year legal guarantee also applies (Directive (EU) 2019/771), covering defects present at delivery, whenever they first show up.
If you're still within the seller's return window, a return or exchange is usually the fastest fix. After that, go through the manufacturer's support team: it handles warranty claims and can often repair the unit even after the warranty has run out. Either way, keep your proof of purchase.
Our public methodology lowers the Nura Score /10 of any model in our Air Quality Monitors guide whose recurring failures show up in owner reviews. A model that breaks down too often never makes it to the top, whatever the brand.
Generally, yes, if you stick to routine maintenance: cleaning, replacing a gasket, recalibrating. Irreversible changes to the hardware are what can cause problems, so read your warranty terms before you open anything up. Anything the manufacturer's manual walks you through is the safe zone.
Your proof of purchase, the exact model name and a record of the symptom: photos, a short video, the sound it makes and any error code. Note when the problem started and what you've already tried. With all that in hand, support can pin down the problem much faster.