The metal chimney on the roof is rusting, about 40 years old. It has not rusted through yet. Can I paint it with black BBQ (high temp ) paint or would regular paint be OK. Not sure how hot it can get when in use a lot.

Greetings all - having an issue with my gas furnace, as fall weather approaches here in Michigan I'd like to get it functioning again. 1. Grand Rapids, MI. Currently in the 60's, winters from 0-40 degrees F. 2. 1923 bungalow, forced air gas furnace. 3. York G8C Model 7516. Model # FG807516MU12A. Installed in 2002 (we recently bought the home, sometime in the span of the last 15 years it was turned from a single owner into a rental unit and was in rough shape, been working non-stop since) 4. Natural Gas 7. Digital thermostat. Details: Came home from camping last week, temps were in the 40's. Decided to turn on the heat to warm up a cold house (should have made sure furnace was clean and ready to go for the first time of the season, my fault). Furnace kicks in, starts blowing warm air, smell something odd (I'm thinking it was dust burning off, the furnace is located in the basement outside of my woodworking shop). Since then it won't complete the ignition sequence and light. So far: Cleaned flame sensor (I don't think this was it, as the flames never light. If it was the flame sensor I believe it would shut off after a few seconds of lit burners) Cleaned gas valve and gas supply (inspected gas supply, checked screens/filters on gas valve, totally clean, no rust/dust on burners or orifices) Furnace has power, gas works elsewhere in the house (stove, dryer, no problems). When I attempt to turn the furnace on and provide heat, everything seems to run fine with the exception of no actual flame. Temp set to 70, vent blower runs, hear the click from the gas valve, ignitor glows red hot, no flame actually starts. Sequence repeats itself 3 times before locking itself out and giving my 7 flashes on the LED. Manual says that there is a problem with the gas valve, ignitor, or flame sensor (thanks, manual). Since cold weather is forecasted later in the week, I have parts that I'm waiting on delivery. New gas valve, new ignitor, and I'm thinking of ordering a new limit switch just in case. Other info: Furnace is clean, filters are new, no obstructions to air supply. If I turn the thermostat to Fan/On, the fans kick on and circulate air throughout the house. The central AC also works if turned on. Currently thinking it could be either the ignitor failing (it glows hot, not sure if it's reaching the proper temp to ignite gas or if the entire surface is heating properly. It's at least two years old, and probably closer to 10 based on the condition of everything else in the house when we bought it). Could possibly be the gas valve, but I'm not sure - I hear the click of the valve when it calls to ignite, but I don't smell any gas at all. Other thought was the Limit Switch (I've been doing some reading and apparently the limit switch can either burn out or lock out the system to prevent overheating? I don't see a button or switch connected that I can hit to reset it). Any advice and help is greatly appreciated!