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Intermittent low level CO readings

Guest Claire

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Guest Claire


I'm hoping someone can advise me as to whether or not I should be concerned about low level CO readings in my living room.

So I have four of the Fireangel CO-9D digital Carbon Monoxide detectors;


  • Bedroom
  • Living room
  • Kitchen
  • Basement (where the combi boiler is)

One of the functions of this CO monitor is the ability to check peak readings within the last month. All rooms apart from the living room are 0ppm.

When I have walked pasted the monitors they all display 0ppm, however last week I checked the living room monitor after around 1month, it stated that's its peak reading was 40ppm. I was concern about this so I had my Gas fire, Boiler and Gas hob serviced and all were found to be working as they should (NB: all are <3years old).

So I thought right, it must have just been a random reading, perhaps I left the living room window was open when I was defrosting the car and it was idling in the driveway.

So two nights ago I used incense sticks to set them back to 0 as per the user manual. When I checked the living room monitor in the morning, it stated that its peak was 35ppm. I  removed the detector from the living room and it returned to 0 without resetting it (dont understand how this is possible).

I then bought new CO detectors, as I thought there might me something wrong with the living room one and set them side by side in the living room.  I was watching TV for around an hour and they both remained at 0ppm however one of them suddenly jumped up to 10ppm for around 20 seconds and then returned to 0ppm. When I checked them this morning both where at 0ppm however they both stated that their peak readings were 11ppm.

What would cause low level readings that last for around 20 seconds?

Could the phone or TV be affecting them?

I know the levels are low and probably wont have any affect, but I find it strange that the peak readings of the other monitors in the house are 0ppm consistently. And I also have young children in the house and don't want to put them at risk.

Many thanks in advance,



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If you have a gas fire in your living room you should have an air brick vent to provide ventilation for the gas fire. Is it possible if the weather conditions are right, that very small amounts of CO from yours or passing cars could be getting into your living room via the vent, which could be happening to your neighbours but because the level was not sufficient to operate the warning buzzer they have not registered a problem?

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Hi Claire

I would by now regard it as likely that you have occasional carbon monoxide present. If you had your gas applications serviced (assuming the engineer was qualified, had a CO meter and checked flues for blockages as well) you need to look for possible other causes. Do you live in a terraced house with neighbours using the same chimney stacks, do the neighbours have flues exiting their building in a location where CO could drift into one of your windows?


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Thanks for your replies.

There is no air vents in the living room as house was built in the 1800s.

The gas appliances were serviced by a Gas safe registered engineer which is also recommended by Which Trusted Trader.

The chimney for the gas fire was noted to be clear on inspection and the lining was checked by the engineer.

We are a semi-detached, however the chimney stacks / flues are not on the joining wall.

The detector in the living room seems stable at 0ppm now, with a peak reading of 11ppm. However I have also noted the detector in the kitchen is normally at 0ppm however I have seen it jump up to 10ppm for a few minutes whilst I've been cooking with the gas hob on. What is the minimum distance the detector should be from the gas hob?

Many thanks,




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