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A CO detector sensor gradually and imperceptibly loses sensitivity. This means it can fail without warning. Take a look at five signs that indicate your domestic carbon monoxide detector is nearing the end of its service life, and find out how to test its functionality yourself.
A carbon monoxide (CO) detector should be installed in all enclosed spaces where combustion takes place. Any combustion appliance and any open flame can produce carbon monoxide if combustion is incomplete. It only takes an inconspicuous burner fault, a blocked chimney, or smouldering ash in a fireplace for a deadly poisonous gas to start forming.
Toxic carbon monoxide is colourless and odourless, and it cannot be detected by any means other than gas detectors. The severity of poisoning depends on the CO concentration and the duration of exposure. At high concentrations, loss of consciousness can occur within just a few minutes.
Particularly high-risk areas include rooms with a gas boiler during the heating season and holiday properties after a seasonal shutdown, when possible faults in gas appliances or chimneys may not yet have been identified. CO detectors should therefore also be installed in cottages and caravans.
This article focuses on detectors for domestic use. Industrial CO detectors are subject to stricter rules and mandatory calibration.
Homes with a gas boiler and holiday properties after a seasonal shutdown are particularly at risk
An electrochemical carbon monoxide (CO) sensor works on the principle of an electrochemical cell. When CO molecules enter the sensor, they are oxidised at the working electrode. This chemical reaction generates an electric current, the magnitude of which corresponds to the concentration of CO in the air. This allows the detector to reliably identify even low concentrations of this dangerous gas.
However, the sensor naturally ages – the electrolyte gradually dries out and the electrodes degrade due to long-term contact with air and the surrounding environment. For this reason, CO detectors have a limited service life. The ageing process cannot be stopped, but it can be slowed down by correctly positioning the detector away from damp, dusty, or extremely hot environments.
False alarms – if the detector triggered an alarm but subsequent measurement did not confirm the presence of CO, this may be a sign of sensor ageing. False alarms can also be caused by increased humidity, chemical fumes, faulty electronics, unsuitable placement, or neglected maintenance.
No response to a test source – the reliability of the sensor can also be tested by deliberately exposing it to carbon monoxide at a precise concentration. Special test sprays are used for this purpose. Never attempt to test the detector using actual flue gases, as this is highly dangerous.
The test button does not trigger the alarm – this is a sign of faulty detector electronics. If the batteries and power supply are both in order, a new detector must be purchased.
Error codes such as END/ERR – gas detectors usually include features that alert you to a fault or measurement error. Error code messages are grounds for immediate replacement of the CO detector.
Weak batteries – if the alarm sound is muffled or intermittent, or the LED indicator light is dim, try replacing the batteries. If that does not help, the detector is nearing the end of its life and must be replaced.
The presence of toxic CO can only be detected using a detector
In domestic conditions, the functionality and sensitivity of a CO detector are tested using two methods: the test button and test gas. Each method checks different detector functions.
|
Button test |
Gas test |
|
|
What does it verify? |
Electronics, power supply, signalling functionality |
Sensor sensitivity |
|
What does it not verify? |
Sensor sensitivity |
Measurement accuracy, some electronic faults |
|
How often should it be carried out? |
Once a month |
After installing a new detector, in holiday properties before the start of the season, or if there are doubts about correct operation |
Table: Differences between the CO test button and CO test gas
A button test checks the functionality of the electronics, power supply, and audible or visual signalling, but it does not prove the sensor’s sensitivity to CO. Ideally, it should be carried out once a month.
Make sure the detector is powered. If it is battery-powered, check that the batteries are not flat.
Press and hold the test button for approximately 3–5 seconds (or according to the manufacturer’s instructions).
Wait for the detector to respond. Usually, an indicator light will come on and, after a short moment, a loud alarm will sound.
Release the button. After a few seconds, the detector should automatically stop the alarm and return to normal operating mode.
If the detector does not respond, first check the power supply or batteries. If replacing them does not help, the detector is probably faulty or at the end of its service life and must be replaced.
Test gas checks the sensor’s ability to detect carbon monoxide. It is a special aerosol or gas mixture with a precisely defined CO concentration that simulates the real presence of a dangerous gas.
Read the instructions from both the detector manufacturer and the test gas manufacturer. Not all detectors are designed to be tested in the same way.
Ensure the detector is in normal operating condition. The device must be switched on, powered, and ready to measure.
Apply the CO test gas according to the manufacturer’s instructions – usually by a short spray near the sensor inlet openings.
Wait for the detector to respond. Within several tens of seconds to a few minutes, the detector should evaluate the presence of CO and trigger an audible alarm.
After the test, ventilate the room and allow the detector to return to normal operating mode.
If the detector still does not respond after the test has been carried out correctly, it is probably faulty or the sensor has lost sensitivity. In that case, the detector must be replaced.
The service life of carbon monoxide detectors is always specified by the manufacturer and usually ranges from 5 to 10 years. Service life is calculated from the date of manufacture, not from the date of installation. Timely replacement of the detector is very important, which is why EN 50291 imposes, among other things, the following obligations on manufacturers:
Every detector certified to this standard must be equipped with a function that alerts the user both audibly and visually when the sensor has reached the end of its operational life. This is usually a specific beeping pattern accompanied by a fault indicator light.
The manufacturer is required to mark the detector housing clearly and indelibly with the date of manufacture and the recommended replacement date, so that the user can easily check its service life.
Once the sensor has reached the end of its service life, the CO detector must be replaced, even if it appears to be working and the test button does not reveal any faults.
The ideal choice is a CO detector with an electrochemical sensor, which offers high accuracy and reliability. The detector should comply with ČSN EN 50291 (for domestic use).
You should also focus on service life, which reaches up to 10 years for some models, and on the power supply method – battery-powered detectors are usually made for domestic use. The alarm sound level should be at least 85 dB. The detector should also include features such as:
end-of-life warning,
test button,
fault and low-battery indication.
A very practical addition is a display, which allows the current or highest measured CO concentration to be shown, thereby making diagnostics and identifying the cause of the leak easier.
The detector should be installed near every potential source, such as fireplaces, boilers, or stoves. In larger houses, however, it is advisable to have several detectors, place them in living areas as well, and interconnect them. This ensures that all of them will alarm in the event of a leak, so you will not, for example, fail to hear an alarm coming from the plant room.
In our range, you will find reliable hazardous gas detectors from renowned brands. For CO detection in homes and holiday properties, we recommend the certified Honeywell R200C-2 carbon monoxide detector with a 10-year service life. For wireless interconnection with other detectors in the building, the Honeywell R200C-N2 carbon monoxide detector is designed.
Reliable Honeywell CO detector from our range
Check the date of manufacture and expiry date on the detector housing.
Check the condition of the batteries or the power supply.
Carry out a CO detector test using the test button.
Check the sensor sensitivity using test gas.
If any of the tests reveals a fault, the detector displays error messages, has reached the end of its service life, or shows any anomalies, replace the detector immediately.
Are you looking for a new carbon monoxide detector for a house, flat, cottage, or commercial premises? Our experts will be happy to advise you on selection, suitable installation, and maintenance for maximum reliability.
The service life of a carbon monoxide (CO) detector is usually 5 to 10 years, depending on the sensor type and the manufacturer’s recommendation. Even if the device is still working and regularly passes the button test, it must be replaced after this period because the sensor’s sensitivity gradually decreases.
Not usually. The test button checks the electronics, power supply, and correct alarm operation, but it does not always verify the sensor’s actual sensitivity to CO. A test using certified test gas can be carried out during a professional inspection or according to the manufacturer’s recommendation.
The button test is an important part of regular checking, but it does not verify every possible fault. You should also regularly check the condition of the batteries, the cleanliness of the sensor openings, the date of manufacture, and the device’s service life. If the detector shows unusual behaviour or is older than the recommended period of use, it is safer to replace it.
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