I did a boiler change today - well, helped out on one. The old one had a leaking heat exchanger, which was dripping water onto the gas burner jets, thus putting out the flame, and leaking out the bottom of the casing.
However, the homeowner thought it was just the pilot light not working - even though it didnt have a pilot light. Because he didnt see the pilot flame, he thought it was the wind blowing in the flue that was blowing out the pilot light. It was a balanced flue, so that is unlikely to happen, even if there was a pilot flame.
So, to stop the non-existent pilot flame blowing out, he put a plastic bag over the flue exhaust. So now, air cannot get in, and neither can any of the exhaust gases get out.
We explained that it was a really stupid thing to do, and he was lucky that the boiler did not work properly, as it could have killed him with the exhaust gases.
He wasnt bothered, as if he smelt the exhaust gases, he would have turned it off!