My mom has a high efficiency natural gas furnace with PVC intake and exhaust pipes going out the back of her house. She thought she smelled natural gas a couple of times in the back yard and had the utility company come out. They didn't find any leaks outside the house, and we have never smelled gas inside the house. I've checked around the furnace area and couldn't smell anything, and soaped the threads that I could access. Today I caught a whiff of what smelled like natural gas in her backyard, and when I stuck my nose next to the exhaust, it was the source. Could what I smelled have been a byproduct of the combustion? Is it normal for furnaces to vent a little gas occasionally? Thanks.

I have a Rheem Imperial 80 Plus that uses a conventional intermittent pilot ignition system. Lately, sometimes after the pilot lights, the spark will stop (as it should, meaning that the pilot has been proven), but the ignition control doesn't send 24V to the main valve for several seconds, sometimes up to a minute. Other times the spark will continue pulsing for a while even though the pilot is lit. And most of the time, the furnace lights almost instantly as it should. I have verified that the flame rod is clean, that the pilot flame is properly impinging on the rod, and that grounding is good. The ignition control is a Robertshaw SP-715A that I fondly recall having replaced on Christmas Eve day ten years ago. Any ideas on the erratic behavior?