Cold weather furnace problem
On New Year's morning our gas furnace wasn't working (13-year-old high efficiency Rheem). Checked the usual suspects, no snow around the vents. It would start, run the pre-purge cycle, then no flame and shut down. When I had the covers off and held the cover switch, it actually started, but would not keep running after I replaced the covers. Since I have a Reliance service contract I called and a tech was promised for the next day. So we used the woodstove and fireplace. Near the end of the day, on a whim, we checked inside the intake pipe and found crusty snow. After poking it out, the furnace started and ran. When the service tech called today before arriving I explained what happened, but he should look at it anyway, since it hadn't been serviced in 6 years. He cleaned out the intake with a brush, checked the furnace over and cleaned the flame sense rod. He also told me if the intake has ice and snow in it, the furnace will run with a cover off using inside air. Good to know. Apparently this can happen in cold blustery weather.