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Over a year ago after a month in our new house, we came back one evening to a cold home and after some googling, I found out that the flame sensor was dirty and the furnace was starting the flame and then quickly puffing it out. I cleaned the flame sensor and everything was normal again for two weeks. The flame sensor would fail every two weeks and every time I would clean it up and put it back in and everything would be okay.

This made me very frustrated, so I talked to a number of HVAC stores, and none had any idea what was precipitating the situation. Finally, a lady at one HVAC store told me it was the lint from the laundry drier that happens to be too close to the furnace and that there is nothing that can be done about it if the laundry machines share a room with the furnace in the basement which is in fact the case in my house. Nevertheless, I bought a brand new flame sensor and replaced my sensor.

The new sensor held up fine for a month and then failed and needed cleaning and started failing every two weeks after the first cleaning. I am now very frustrated and concerned about what would happen if I was to go on a prolonged vacation in winter. This would specially be a problem since my spouse is not handy and she would simply have to freeze waiting for an HVAC technician if this ever happened while I am away.

Is anybody else having the same problem?

Is there an easier longer-lasting solution?

I should mention that my furnace is high-E newly installed Goodman furnace running on natural gas in mid-western Canada (3 years).

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    3-year old newly installed furnace? Call the installers. I'm hoping you have some sort of warranty or similar. Might be time to reposition a machine or two, though I'm not quite convinced it's lint from the dryer. Consistent lint anywhere around a furnace isn't a good idea.
    – alt
    Dec 18, 2014 at 23:41
  • The dryer should not be spewing lint into the house, so I wouldn't suspect that's the cause. More likely, your gas is not burning as efficiently as it should, and is producing more soot than normal. Is there a drip leg on the gas line, near where it enters the furnace? Does the furnace have an adequate source of combustion air? You could also try contacting an HVAC company, or your utility to check for excess moisture in the gas supply.
    – Tester101
    Dec 19, 2014 at 14:55
  • It could also be that the sensor is positioned incorrectly. It may be designed to be slightly back from the flames, not directly in the flame (contact the manufacturer, or refer to the documentation).
    – Tester101
    Dec 19, 2014 at 14:57
  • How does the flame look? Is it nice and blue, or more orange/yellow?
    – Tester101
    Dec 19, 2014 at 19:20
  • Hi everyone, thanks for the comments and the reply. The flame has a nice blue color. I checked the air intake and the exhaust and they both seem in perfect condition. My gas bill is not unusually high, but this is a very small house and an inefficiency in the combustion system might not be evident in the gas bill. The period of sensor failure has now been reduced to every other day. I think I will call a gas technician to go over the combustion system after the holidays. But until then, any ideas?
    – Essi Shams
    Dec 25, 2014 at 15:03

7 Answers 7

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Have you had a gas technician go over your entire combustion system?

I strongly suspect that something is not adjusted correctly, and you have excess soot production (lint seems like a red herring, frankly) which is making the sensor "dirty." It also means you are not burning your gas as efficiently as should be possible. This is almost certainly a problem with combustion, not the sensor. The sensor fouling is a symptom, not a cause.

I don't really regard this a great area for DIY - without the right tools, which cost more than most homeowners (including me) will spend, and the right training to go with them, screwing up combustion appliances though self-service is more common than tuning them perfectly. There's also "not creating a giant loophole for your insurance company if the house burns down" as a minor factor in that thinking. Having burners professionally serviced on a yearly basis is a minor expense, comparatively.

If (as is commonly the case with high-efficency burners) the furnace has both an air intake from and an exhaust to outside, the dryer lint really can't be the problem. Some sort of blockage of that intake could, however, potentially cause the problem you are having (insufficient air supply causing a rich, sooty flame; soot fouling the sensor.)

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  • Hi , thanks for the reply. The flame has a nice blue color. I checked the air intake and the exhaust and they both seem in perfect condition. My gas bill is not unusually high, but this is a very small house and an inefficiency in the combustion system might not be evident in the gas bill. The period of sensor failure has now been reduced to every other day. I think I will call a gas technician to go over the combustion system after the holidays. But until then, any ideas?
    – Essi Shams
    Dec 25, 2014 at 15:03
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The flame sensor is only as good as the circuit board it plugs in to, that "thinks" about what it's getting. Have you considered that the control board might be goofy? They do go bad, too.

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After cleaning the flame sensor, checking ground wire, checking exhaust for cracks or blockage and the board connection which did not fix it. We found that the hanger on the exhaust pipe was hung poorly and causing exhaust pipe to droop down which made it hold condensation that ran back into unit which shut the furnace down. Fixed hanger to make exhaust pipe level and it seems to be working now.

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Could also be that your thermostat is no longer sensing the correct temperature and causing your furnace to remain on longer in the heating cycle than usual. This causes the burner to heat up the flame sensor and cause it to become dirty sooner than just a yearly maintenance. Also, is it a 2-stage induced draft motor? When your furnace comes on initially, does the small motor (induced draft motor) come on loud and really fast? If so, then its immediately starting in 2nd stage which should not happen. This opens up the gas pressure on your gas valve and allowing high burner operation and giving your flame rod more flame and causing it to also become dirty sooner.

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Phosphates from your washing machine detergent are plating on your flame sensor. Get your combustion air from outside and problem will be solved.

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  • The combustion air is being taken from outside.
    – Essi Shams
    Dec 20, 2016 at 21:25
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By law you should have furnace in big enough area to consume proper air flow. 50 cu ft/1000 hr btu. If your furnace is 80000 btu you need 4000 cu ft of space. Room size X ceiling height is actual cu ft. If you have a hot water heater and dryer in same room you will have to add that btu rating to the calculation. If you don't have 2 pipe furnace and don't have correct spacing it will cause incorrect combustion. Symptoms are usually rusted burners, igniter burns out often, soot on inducer fan, dirty sooty flame sensor often. As far as flame sensor testing a qualified tech can check with a meter DC micro amps output and see if flame sense is sending signal to the board for approval to keep gas valve open.

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Another possibility of dirty flame sensor often is chemicals near by, cat liter box, and smoking meth in the house. White substance usually noted on flame sensor. This is not a joke...smoking meth incident actually happened with one of my instructors.

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