I've always spent hours down here every day and it never did this before, just sometimes the dull LP odor, but no leaks or CO. But now some days I get a very strong maple syrup smell. Even though the boiler isn't even powered up, and I see nothing wet around or at any pipes, just reddish stains in the conrcrete from leaks before I was here. This has been going on since last year sometime. Is that by chance what boiler antifreeze smells like? The previous owner said he put antifreeze in it. It doesn't smell like car antifreeze. All unfinished. It's quite clean. No critters or mold down here. I run a dehumidifer. Never freezes.