I'm about to go look at a friend's furnace tomorrow morning. But what he described over the phone is not something I've ever seen before. Just thought I'd check with you guys for what I should look at first, assuming I can duplicate the problem. He says that when the furnace kicks off, it will not kick on again until he turns the thermostat to off and then back to heat. And he says it works fine during the day, but only has this issue at night. He replaced the thermostat with a Nest and the problem persists. Says it been like this for over a week now and wakes him up cold in the middle of every night. This is a natural gas furnace built into the air handler for the split air conditioner. I'll know a lot more details about the specific machine when I see it tomorrow morning, but thought I'd ask if you guys have any ideas on what would cause this kind of intermittent issue.

Have a question. I have an AeroFlo furnace. 3 years old. The ignition lit but the flames wont come on. I can hear the fan and motor running. The ignition lit and shuts off when no flames comes on. After the third time it lit on and no flame comes the system shuts down and I get the 7 red light blink "lockout due to ignition" However, sometimes I shut down the main disconnect and turn it on again and sometimes it start working for a while. after it goes to stand by it wont turn again. What Can I check? I tried using a sand paper on the stick flame sensor but still. Tried blowing the hoses but same. What else can I try or check? Thanks!