This morning it was cold in the house. The furnace blower was running but it was blowing cold air. I checked the thermostat and it said 61º. Uh oh!! I checked it and there was no fire in the heater box thing with the little viewer window.

I know to shut down the furnace and check the LED for error codes turning it back on so I tried it. I shut it down for a few minutes and started it back up. No error codes, it just started working normally again. Why would it blow with no fire in the heater and then start working again after shutting it down and turning it back on again (just like the good ol' IT stalling technique for computers)?

It's been working normally all day but is there anything I should watch out for?

If you turned the power off, you cleared the fault code and reset the control board. There is several possibilites for the fan to operate with no flame.
Glad your heat is back on line in this weather.

Gas heater? Probably the pilot got blown out (by a backdraft perhaps) and wasn't heating the thermocouple so the gas turned itself off. I'm thinking this should have shut down the blower too, but who knows? Maybe a mis-wired thermostat?

More attributed to old gas furnaces are "short cycling" due to extreme cold and long run times where the heat exchanger gets real heat soaked, and does not cool down before the next call for heat, and that creates a natural draft of more fresh are, resulting in a "delayed ignition" when the gas comes on, and you may get a "whoomp" and the flame rolls out, sensor cuts gas supply, and the fan continues to run on.

Backdraft from strong wind or gust.

Newer units should be better able to deal with it.

Cracked heat exchangers are also notorious for issues with gas furnaces. (again, more familiar with older units)

If you have CO detectors and do not get any "explosion" delayed starts, and it is very rare, then I would simply mention it next time you get it serviced. Calling in the middle of cold snap is going to be ex$pen$ive.

Hope it was a onetime event.

My gas heater is a 1983 model Rheem, and I have been having a fit with it short cycling.

I have checked everything except the heat exchanger, as it has been in the teens to 30s for the past week it's been acting up, so I cam not going to tear it down as I do not want to risk breaking anything and not be able to use it at all.
(Someone did some work and replaced some components but it looks like hack work, and I never thought to tear into it as it worked fine for two winters)

So, I run it for about 20 minutes and shut it down for an hour, turn it off when I go to bed and when I wake after about 4 hours, run it again , back off and back to sleep.

Open all south window blinds and I can get by in low 60s in the house just fine.

When it warms up, I'll tear into it and see what it needs to make it correct or replace it.

Thanks, guys. That sounds like the issue. It’s been pretty cold and windy. The furnace is pretty old.

Flame sensor dirty?

Sounds like the electronic ignitor. Happened to my furnace early last year. Easy fix, if you have the part. i.e. for a furnace repairman.

quote:

Originally posted by djinco:
Sounds like the electronic ignitor. Happened to my furnace early last year. Easy fix, if you have the part. i.e. for a furnace repairman.

This is what I was going to suggest, take a look at the ignitor. I had to have mine replaced a few years ago for the same reason.

Oddly, ours acted up today. Fan running, and blowing cold air. Shut it down at the breaker, waited awhile, and turned it back on. Same thing.

Fortunately, we are on very good terms with our HVAC guy. I called him (on a Sunday, while he was watching football), and he walked me through some tests I could do and which wires to bypass sensors, so we could narrow it down. Turns out a sensor wasn't working, and he is ordering another for me. Once I got the sensor back in (after giving it a few taps and working the button on it back and forth multiple times), all is working again.

All that to say, could be a wonky sensor, getting ready to fail. I hope it isn't, and was as the monkey described.

Stay warm!

We just had the ignitor replaced in one of our rental houses. Property manager was trying to push me to buy a new heater.
I had them send out a vendor who had done above-and-beyond work for me in the past. Ignitor replaced; should work for years yet.

We had an issue last week with a 6 year old furnace short cycling and not keeping up with heat when the temps dropped to single digits. Continued for several days so we finally called for service as the loft involved wouldn't get above 60 degrees and is my wife's work office. Technician found the exhaust full of dead lady asian beetles and found they'd also left debris on some sensors. 30 minute clean up job for him and it ran like a champ afterwards. They usually flood our area in mid-October to early November so they showed up after the fall service call had been done. Might be something to check on as I believe those pesky things cover a good portion of the country these days.