Odd smell in the basement

A friend had a new gas boiler installed last winter. Over the past few months, she noticed a smell (something like oil) in the basement that comes and goes. She called the boiler people, who said there's nothing wrong with the unit, but suggested that maybe her neighbors had poured oil into their basement sewer and it had backed up into hers. She had the sewer line rodded out; the plumbers discovered a cracked drain pipe and replaced it. But the smell comes back occassionally, regardless of whether the boiler is on.
She's thinking maybe the vent for the boiler and/or hot water heater is blocked.
Any other suggestions on what to check?
Karen
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(OperaBufa) wrote:

That wouldn't produce an oil-like smell.

I bet the traps in her floor drains have dried out. It's a common occurrence in wintertime, when the humidity is lower. Have her pour a bucket of water down each drain, and see if that takes care of the smell. If so, a gallon of water in each drain, once or twice a month, should prevent a recurrence.
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Get a Co meter-alarm, Nighthawk makes one that includes a Ng gas leak alarm. It could be a dry trap, a sump pit, or is it possible the bldg used to be heated by oil, then likely oil spilled , that is a problem I have presently
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OperaBufa wrote:

If refilling traps doesn't cure it, ask the gas utility to come out for a "gas odor" complaint. If the source is a combustible, their test equipment will track it down.
Jim
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