My boiler started doing this and it turned out to be the Fan that extracts the carbon (what ever) out of the chimney. As this is poison it eventually shut down as a safety measure. After calling a heating firm they had to order a new fan, monday, which was delivered to them Wednesday and is being fitted tomorrow Thursday. Cost around £290. May take out Maintenance Contract for £110 also.
Joan and Tony Bradley (aged 65)
February 2009