For those who followed or helped with my gas boiler panic on Saturday night, I thought I would provide an update.
- I am still alive.
- The heat exchange was caked in soot, the plumber who looked at it reckoned it hadn't been cleaned in at least 10 years. He had to scrape the soot out from between the fins. I expect this didn't help the efficiency of the boiler much!
Good news. However I would advise you to make regular spillage checks to ensure the fumes or products of combustion continue to go up the open flue. Pop into a merchants such as plumb centre and buy a box of smoke matches. these provide a source of visible smoke to carry out the test with
The caking in soot happens very quickly once it starts, probably in just a week. Something starts it off, such as one burner getting some dust in its airhole which starts depositing small amounts of soot. Some of this falls off, blocking the airholes of other burners which start producing soot. Also, this soot starts blocking the heat exchanger, reducing the draft and the airflow into the burners, all making more soot. It's a runaway process which feeds itself.
Lack of cleaning leads to a build up of the dust which is thus more likely to get sucked into a burner airhole. In your case, the initial trigger could have been blocking that air vent, reducing the draft and airflow at the burners, resulting in the generation of the initial soot.
Suggest cleaning/repainting the walls/ceiling, as the sooting up of those was something you noticed, and you might not do so again if they're already sooty. If the room lends itself to a few pot plants, they can be a good early indicator of fumes too. When my parents had a similar problem many years ago, the first sign was that all the house plants started chucking off their leaves. I suspect that might have been one of the normal combustion products such as sulphur dioxide, as a CO detector didn't detect anything.
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