Hello! I have a furnace conundrum and am looking for ideas.

My 8 year old Goodman/Amana single stage gas furnace (Model GMS80904BNCC) intermittently and randomly loses its flame, then reignites. I am near Denver, CO and our temps are in the low 20s this week. The furnace is in a large laundry room in the basement of a ranch style house. It is not next to the dryer and does not have a lint issue. The thermostat is a newer Honeywell programmable.
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The furnace starts up normally. Tstat calls for heat, induction fan starts, hot surface ignitor glows, and the four flame jets ignite, burning strong and mostly blue. The blower motor kicks on and everything runs fine - until it doesn't.

Rarely the furnace makes it through the cycle and shuts down normally once the tstat is satisfied. But usually it misfires at least once, often several times. When this happens, the flames suddenly cut out. A few seconds later, the ignitor glows in an attempt to relight. Sometimes the burners light back up on the first try. Sometimes the ignitor will glow and go dark again many times (I have counted ten) before it successfully relights. Each time it glows, you can hear a clicking sound along with the induction motor revving up. It keeps trying until it eventually relights, then limps along like this until the flames go out again or until the house finally gets warm enough for the tstat to stop calling. The blower motor never stops until the end of the cycle.

It is not windy outside. There is no odor of natural gas, and the CO detectors are at zero. The furnace never locks out, and the led on the control board never shows an error code. You'd never know this is happening unless you happen to be within earshot of the furnace to hear the POOF sounds of the flame continually cutting out and reigniting.

We changed the filter. We cleaned the flame sensor, and when that didn't help we replaced it. An HVAC company told us over the phone that the symptoms would make them suspect the control board. It had no visible burn marks or damage, but we replaced it anyway since it wasn't expensive. No change. The hose to the pressure switch is not clogged, and if you pull it off during the cycle, the furnace shuts off like you'd expect. Neither of the blower motors are making any unusual noise. I don't think this furnace could have condensate issues - I can't find any evidence of a drain line.

Here is a video showing the issue. It happens about 15 seconds in, then again around 1:40.

https://youtu.be/-H-Ihu-A_To

What could be causing the flame to cut out like this? Any suggestions are much appreciated. Thank you!

 

What trouble codes are you getting on the control board??

 

Have you ever had your 8 year old furnace serviced ?

In your video..... That is either a control board problem or the thermostat.
The only way to confirm is to put a voltmeter on the W and C terminals during a call for heat.

In the beginning..... the burner and the inducer where going off together. That points to the stat.
Towards the end.... the burner was failing and the inducer was still running.
Upon further review....... that looks more like a control board failure.
The restart time is incorrect.
The purge times are incorrect.

It still wouldn't hurt to look thru the sight glass in the blower door to see what fault is being set.

 

We bought this house 3 years ago, and had a preventative maintenance done about 2 years ago.

The control board shows a solid red LED, which according to the list inside the furnace means "normal operation." But just in case, we swapped in an OEM replacement control board, and it is still doing the same thing.

 

Please don’t just start swapping parts. It waists your money and risks not fixing anything.
Using your meter, check for a constant heating call from the thermostat.

 

I tried jumping out the thermostat and the problem continued so I knew it wasn't that.

It turned out to be the pressure switch. I had tested resistance on my meter and it seemed ok. Someone on another forum pointed out that the switch could be functional but WEAK, causing the intermittent flame outs.

I realize that swapping parts isn't the ideal way to diagnose, but the total cost of the control board, flame sensor, and pressure switch was less than what I'd pay for an HVAC company just to show up. If one of these three didn't fix it, the next step would have been to bring in a pro.

Thanks to all for your suggestions!

 

I’ve only ever seen a handful of pressure switches actually fail.
Most of the time they are clogged up and just need cleaned out.

 

The tube from the inducer was clear and I couldn't see any way to open up the switch itself without destroying it. How do you clean one out?