Cleaning a furnace flame sensor.
January 19, 2014 8:47 AM   Subscribe

My furnace is cycling on and off continuously. I'm pretty sure I know why and think I can handle the repair (cleaning the flame sensor), but I want to be sure I'm doing it properly.

I've got a Goodman gas furnace that's approx a year and a half old. It recently began a process of firing up, then immediately the burners shut off. It does this steady. Based on online research, I'm 98% certain it's caused by a dirty flame sensor. Here's my plan:

1. Shut the power to the furnace.
2. Open it, locate the flame sensor, dismount it and clean it.
3. Close the furnace up, put the power back on and hope I've solved the problem.

One thing I'm a bit worried about is the gas - is it necessary to shut it off beforehand, then open it after the repair? Online guides aren't mentioning this. I'm concerned that shutting the gas off will cause a further problem and I'd rather not shut it off.

Is my plan correct?
posted by davebush to Home & Garden (8 answers total) 1 user marked this as a favorite
Do you mean shut off the gas outside at the meter, or the local shutoff valve on the furnace unit? It seems you could execute the cleaning with the local valve off *and* the power off at the circuit breaker just so the thing doesn't try to start while you're working on it.
posted by JoeZydeco at 9:15 AM on January 19, 2014

I meant the local shut off valve. I'm just a bit concerned that shutting that valve will somehow introduce a problem later when I open it - I'd rather not interrupt the flow if I don't need to.
posted by davebush at 9:50 AM on January 19, 2014

You won't be opening any part of the gas line to get at the flame sensor. It's probably not absolutely necessary to shut it off, but neither is it likely to hurt anything. It's more important to switch the furnace off electrically before you go mucking around in there.
posted by jon1270 at 10:01 AM on January 19, 2014

If the power is off to the furnace, you should have nothing to worry about regarding gas accidentally flowing. I have never seen a furnace repairman turn off the gas to the furnace before opening it up. I would, however, ask yourself whether or not your cleaning of the flame sensor might potentially damage it, and/or what might be causing your flame sensor to become dirty. A properly-operating furnace that's combusting correctly shouldn't be gending up with a dirty flame sensor, and while cleaning it may result in it being OK for now, it may result in bigger damage in the long run. (It may also not be the problem - I've seen cycling on/off behavior due to condensation in a vacuum/pressure hose.)
posted by jferg at 10:06 AM on January 19, 2014

Update - it worked. I cleaned the sensor and it fired up fine. Running smooth now. From what I read online, the sensors tend to get carbon build up and it's pretty common.
posted by davebush at 10:17 AM on January 19, 2014

Glad to hear it worked but take jferg's advice. Find a furnace tech that can analyze your flue gasses and make sure the combustion is correct.
posted by JoeZydeco at 10:39 AM on January 19, 2014

There was a surprisingly small amount of build up on the sensor, but enough to cause the problem apparently.
posted by davebush at 10:45 AM on January 19, 2014

Call your gas company and see if they will come out to check it for free. I had the gas value go on our furnace - I fix most stuff myself but don't fool around with I called the service line for our gas company to ask for a referral and they indicated they contract their own techs so I had them send someone out to look at the problem.

He checked it out, confirmed it was the valve and indicated that the part would be $30 and that he had it is his truck. When I asked about labor he said - free, it's all part of your gas bill. (We don't pay for any other service contract by the way).

Apparently from a safety perspective it's better for the gas company to pick up the cost of the labor to ensure that people keep things running safely...when I asked why everyone wouldn't call the company directly he indicated that some people just don't know to call and/or they have their own people to do the service...

All that said if the blower died I'm sure they wouldn't touch it, but if its on the gas end of a gas furnace I'll bet they would do a routine check for free...
posted by NoDef at 1:23 PM on January 19, 2014

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