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Gas Safety Week: How would you know if your boiler was dangerous?

Warning signs that your boiler may be leaking carbon monoxide

So far, during Gas Safety Week, we have reinforced how important it is to service your boiler every year and given advice on how to maintain your boiler well to avoid CO emissions but today we’re looking at the signs that could indicate that your boiler may already be dangerous. Any one of these could be a cause for concern and should be referred immediately to a Gas Safe engineer.

A strange smell

If there is a faint smell around the area of the boiler, this could be an indication that something isn’t right. CO itself doesn’t have an odour so that’s not what you’re looking out for but an odd smell could mean that your boiler isn’t burning properly, and that is when you are at danger from CO leaking.

Boilers can often be in areas that may already be quite ‘fragrant’ (kitchens, bathrooms etc) which could mask smells coming from the boiler. If this is the case, make a point of giving your boiler a sniff every now and then, especially late at night or in the morning when other scents are less likely to be present.

Black stains

The flue is designed to direct fumes outside of the house but if that’s not happening and those fumes are being emitted from the boiler into the home, they can potentially cause black stains around the boiler – most commonly on the ceiling above the boiler.

When you clean the room the boiler is in, make a point of cleaning around it and taking note of any discolouration. That should allow you to notice anything changing quickly.


Condensation in the room where your boiler is can be a sign that the boiler is not being vented properly. If it’s in a large room, it can be harder to notice this so perhaps keep a mirror or picture frame near the boiler that would show condensation in a more obvious way.

Pilot light blows out or changes colour

The pilot light in a combi boiler is a gas flame that you can see within the boiler. The boiler won’t work if the pilot light isn’t on. The pilot light can go out for a number of reasons and often can be re-ignited yourself. However, if it constantly seems to blow out it may be an indication that the gas is not fully burning and this can increase the risk of the presence of CO.

Flu-like symptoms

CO can kill very quickly if there is a significant leak (though as little as 2% in the air can do this) but low level poisoning can manifest itself in symptoms that are very flu-like in nature: headaches, sickness, dizziness, fatigue etc. If you feel like this at home but feel fine when away from home that can be an indication that something isn’t right.

CO monitor bleeping

This seems too obvious to point out but you would be surprised how many dismiss an alarm of this kind and put it down to low battery. The sound a CO monitor makes when it detects CO is very different to a low level beeping it makes to show low battery. Press the test button to hear the difference and if it does go off, don’t just remove the batteries and ignore it.

If you experience any of these signs then call in a Gas Safe registered engineer as soon as possible. For more information about preventing a CO leak, look back on our blog from yesterday.

This blog has been produced as part of our Gas Safety Week 2019 campaign. See more information about Gas Safety Week here.

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