Our natural gas boiler is about 30-40 years old (manufactured 1987, first service sticker was 1994, so I assume about 35 years old). It's in our unfinished basement. A few months ago we had the entire basement (walls, floors, ceilings, exposed piping) painted and there is still a mild paint smell. Since we started using the boiler this winter there is a light campfire smoky smell that starts going through the basement after the boiler's been running for 10-15 minutes. All the burner flames are blue and I just drained the expansion tank this morning due to it not maintaining water pressure and losing water from the TPR valve. We have a combination smoke/CO detector on the other side of the basement and it hasn't gone off. This didn't happen last winter at all. I might be imagining things but it seems to be most prevalent in the areas right under the hot water piping - both the PEX from the boiler and the hot water lines into our bathrooms and kitchen. I don't get as much of a smell from the boiler itself. Could this be from paint on the pipes, or the joists that they're on, heating up and creating fumes? FWIW this smell dissipates when the boiler's been off. We turned the heat off overnight so I wouldn't scald myself in the expansion tank drain this morning, and there was no smoke smell. After I completed the drain, refill, and started the boiler again the smell started about 15 minutes later. Thanks for any advice. I'm obviously concerned but don't want to worry unnecessarily.