Anyone know anything about gas furnaces?

[mnc2fan]

We've been having some issues with our gas furnace. Most times when the thermostat goes below its target temp turning the furnace on, but the burner doesn't light. Thhe ignitor heats up tries to light the burner, but instead of it lighting it just shuts the gas off. Then just blows cold air through the system for a few minutes, shuts off and it tries to light again. Sometimes going through this cycle 3 or 4 times before finally lighting.

The furnace is 13 years old, and uses a hot surface ignitor. The thermostat we use is programmable. We just bought the house, so we have no idea of what has been replaced, or if the other owners were even having problems with it.

[txarkitekt]

Sounds like the ignitor is failing. There is obviously gas in the system...cause it finally lights.

There also could be the possibility of a carbon build up at the ignitor. The build up prevents the ignition of the gas--and it take a few times for the carbon to heat up enough for the gas to light...

[Vince_B]

I'm thinking of one of two issues. If the furnace does not light the gas or the gas does not even start to flow, a bad gas valve could be the issue. As long as the igniter is glowing red it is not the problem. If the furnace does light but shuts off very soon after, clean your flame sensor. I actually do this once every year because being in the north our furnace gets a lot of use. I would try to clean your flame sensor and make sure you have a clean filter in there. To clean it use very fine sandpaper, scotch bright, or steel wool. Also your furnace might have a diagnostic trouble light in it. Take a look around. Hope this helps. Vince

[PurpleMinivan]

Standing pilot or electronic ignition? Sounds like the thermocouple or flame sensor is going out. You can try and clean it up with fine sand paper or emory cloth if you have it. I would replace it with a new one ASAP, you don't want to get caught without your heater when you really need it! Google Johnstone supply in your area... they should have what you need for cheaper and just do it yourself for about $30 instead of paying someone $230 to do it. Post up in here if you need help walking you thru the changeout.

[metalchips]

I'm thinking of one of two issues. If the furnace does not light the gas or the gas does not even start to flow, a bad gas valve could be the issue. As long as the igniter is glowing red it is not the problem. If the furnace does light but shuts off very soon after, clean your flame sensor. I actually do this once every year because being in the north our furnace gets a lot of use. I would try to clean your flame sensor and make sure you have a clean filter in there. To clean it use very fine sandpaper, scotch bright, or steel wool. Also your furnace might have a diagnostic trouble light in it. Take a look around. Hope this helps. Vince

+1

Look for a blacken round rod about 3/16" in dia. about 2" long. It should be shiny. It has a wire on the base end going to the control box. It generates current from the flame, if it is dirty it does not send current so the control thinks there is no flame and shut off the gas.

[hunt4game29]

Like people have said if your ignitor is glowing red when the heater starts and the gas valve is not lighting then i would say the gas valve is sticking. Some times comes on some times wont. (i just had on do this last week and the valve would some times work and some times not.) Next time it does it try and tap on the valve and see if it starts. If it does then replace the gas valve. If it does not seem to work when tapping then check when the ignitor is glowing and see if you get 24volt to your gas valve if you do and the valve is not opening then replace the valve. Most gas valve run around $50 to $100. Either take it off and take it someone and get a new one or right the model number down and get a new one. If you dont have 24volts then back trace it and see if all your safety's are closed and not opened most of them should om out closed with a tone. If you need any other help let me know.


If the flames are lighting for and little bit and then shutting off then like others were posting the flame sensor is either dirty or going bad.

[mnc2fan]

I'm posting up a vid. After looking I'm not seeing a rod that would look like it is just for a flame sensor. But the ignitor looks like it could be the sensor. The first few seconds of the vid, you can't see it but the gas for the ignitor is on.

[metalchips]

flame sensor
It has to be your flame sensor. Can you clean the two circular thing a bops that are on the left and right? Maybe thats the flame sensor. I have never seen them before.

Keep warm

[hunt4game29]

The round things are flame roll out switchs/ high temp switchs if they get two hot it shuts the gas off to the gas vavle. Now it almost looks like when it first trys to start the gas valve is not putting enough gas out to light all three burners. Have you tried to hit the gas valve when the first one is burning. If it was a flame sensor then all three burners would come on and then go off a little while later.

[hunt4game29]

Also check for me if when it does this check the 24volts to it.