A neglected boiler..
This boiler had been on a service contract but hadn't been maintained properly. As a result the heat exchanger had completely sooted up, not even allowing enough combustion air to maintain a pilot light !
The only reason the customer hadn't been subjected to high levels (lethal in fact) of carbon monoxide was due to the boiler being of the 'room sealed' style, ie. all products of combustion
were being flued direct to outside air.
Please do not neglect to have your Boiler Serviced and have Gas Safety Checks carried out annually.