Well we have gas powered heat and stove. But here's the reasons I'm pretty sure it hasn't leaked. We'd smell it because they put a strong smell in gas so people know when it has leaked.
Just a quick note hon, carbon monoxide's completely odourless, it's not gas but a byproduct of when gas is burned in an old or faulty appliance - that odourlessness is precisely why it's so insidious & dangerous. Hopefully it's not your issue here but I'd be remiss if I didn't bring it up - I refuse to attend a house to de-haunt/"exorcise" it (and I do A Lot of dehaunting and exorcising houses - plus flats, bedsits, even once a kennels!) unless the occupants have checked for this and ruled it out, because it can mimic(/invite?) many symptoms of psychic attack and haunting.
More info here - http://www.bbc.co.uk/health/conditions/carbonmonoxide1.shtml
I've been smoking a lot, and I think it made it worse. Maybe it is something like that. When I was trying to go to sleep and found myself in my bed--I was then conscious of a force of evil. The evil spoke to me. Said things, that I don't fully remember because I became dazed upon waking. I remember it slightly. Basically he was telling me how he was boss and not to mess with him. I don't think he attacked me, he just provoked me and created utmost fear. It seems like a he, but not quite a he- kind of like a non-gendered force. So I call it, it too. Because I don't know any other way to describe it. I stood up in the dream, I said earth water air fire, and envisioned the elements, then I tried the LBRP, I was scrambling to it because I was being tortured by it. Then I evoked all the names of the Gods- Yahweh, Elijah, Elohim, and anyone I could think of...I don't know what I should have said. BUT IT WORKED. I also said- Go back to the source! It simply stopped, but it took several false awakenings or getting up in the astral until I finally woke up. That was probably the most terrifying nightmare I've had in several months...or even my whole life. It was really messed up and Satanic.
But also that night I had smoked some cigarettes, and I think that could have been part of the cause.