Gas and Oil Home Heating Furnaces - Furnace starts and stops (with video!)

Hello. Having a little trouble with my furnace. Brand is unknown, no markings, but it might have something on the right side, but there is no way for me to look.

What happens is that the pilot will light. Warm the flame sensor enough to start the burner. But as soon as the burner lights, everything shuts off. Then the pilot re-lights, warms the flame sensor (thermocouple right?) light the burner, then shut off.
Here's what it looks like, you might need Quicktime to view it, sorry its a crappy cell video, but you get the point of whats going on through it.
http://www.kneedragger.net/Furnace.3g2

Lucky for me it's our upstairs furnace and we only sleep up there..
Now From my reading it sounds like the limit switch (I have also read of people calling it a high temp switch). I'm assuming I should jumper the switch and see if that does it. Then I know where to start. But of course wanted to check with some pros before I start shorting out connections close to a gas line... I have a Honeywell limit switch, i left the modem number at home. But it looks like this when opened http://www.kneedragger.net/honeywell.jpg
I'm thinking that in order to jump the connection I just connect the two wires coming out of the "limit" side, right?

If that fails what else should I be looking at?
Thanks for your help
Adrian

No need to fiddle with the fan & limit control. That is not the source of the problem. Remove & clean the flame sensor with Scotch Brite. Do not use steel wool or sandpaper. Reinstall the flame rod & let us know the result.

Cleaned all nice and shiny..Same thing. Thanks for getting back to me though.

God it been soo long since I've been around this type of valve...

I am pointing at the "flame sensor" where this tube goes to top of the gas valve to sense the pilot light, and when it's hot then it will turn on the gas valve.

If it is really a thermocouple, which it looks like it might be, then make sure where it screws into the gas valve is tight, and make sure flame stays engulfing the thermocouple when the burner comes on. I bet it is not. The burner coming on may be sucking the flame away from the thermocouple, due to increased up draft up the chimney or from the general flow of the wind in there following the flame of the burners going upwards, rather than outwards, toward the thermocouple.

Sometimes you can subtley bend the thermocouple end to get it closer to the hood to stop this. Or turn up the pilot adjustment, as there should be an adjustment screw on the gas valve under a larger cap screw, sometimes.


Or replace the thermocouple and see, as they are cheap. But this will not help you if the flame is being sucked away from it.

If it is really a thermocouple, which it looks like it might be, then make sure where it screws into the gas valve is tight,

E, It's not a thermocouple set up.. It looks liek one, but it's not.. It has 3 pins and plugs into the gas valve, not screwed into..

I am drawing on a blank what this valve set up is called, and can't find it on google since I don't know what the proper name of this type of set up.

Jay,

Okay. But since it is related to the gas valve and not electrical related as a flame sensor is that plugs into a control board or module, I bet it works the same as a thermocouple, and the flame has to be engulfing it. I believe it is an engulfing issue. All too common with gas asppliances, even water heaters, for this to happen right when the burner comes on and the direction of the pilot flame changes a hair.

Shouldn't you be at work? - like me? :cheshire:

E, It's not a thermocouple set up.. It looks liek one, but it's not.. It has 3 pins and plugs into the gas valve, not screwed into..

I am drawing on a blank what this valve set up is called, and can't find it on google since I don't know what the proper name of this type of set up.


Would a high rez photo help you at all? I could take a pic of anything you want.

Shouldn't you be at work? - like me? :cheshire:

Nope! Not till next Thursday! :cool:

Well, I tried adjusting the pilot light. It didnt seem to do anything. I even tightened it all the way down and it didnt seem to do anything to the pilot light.

Ok, had to dig out my old school books, and what you got is a cycling pilot ignition system. I think the "plug in mercury flame sensor" may be your issue.

Do you have a meter?

not right now, but I could get mine back from my dad in an hour. When I do, what should I be looking to test. like I said, I can take some high rez pics of anything you need.

When you do get the meter, set it to OHM scale.

Unplug the the sensor from the gas valve.. There should be 3 terminals, labeled 2, 3, and 4.

You should have continuity between 4 and 3 when the sensor is cold.

More importantly, you should have continutiy between terminals 4 and 2 when the sensor is hot.

Let the pilot light and heat up the sensor for a minute and check for continuity between pins 4 and 2 on the sensor. If no continuity, then then mercury flame sensor needs replaced.

When you do get the meter, set it to OHM scale.

Unplug the the sensor from the gas valve.. There should be 3 terminals, labeled 2, 3, and 4.

You should have continuity between 4 and 3 when the sensor is cold.

More importantly, you should have continutiy between terminals 4 and 2 when the sensor is hot.

Let the pilot light and heat up the sensor for a minute and check for continuity between pins 4 and 2 on the sensor. If no continuity, then then mercury flame sensor needs replaced.


Well, I let it heat up and got nothing on 2 and 4. You sure theres nothing else it can be. I could have swarn my brother replaced that last winter at a cost of 80 bucks or so.. Ahh well. I'll let you know if that works. Thanks

If we are indeed talking about a white-rodgers flame sensor, you can test the valve by: unplug the flame sensor..install a jumper in holes 3 & 4..pilot should light....now take the jumper and install in 2 & 4..main burner should come on..remember thermostat must be calling for heat.

If we are indeed talking about a white-rodgers flame sensor, you can test the valve by: unplug the flame sensor..install a jumper in holes 3 & 4..pilot should light....now take the jumper and install in 2 & 4..main burner should come on..remember thermostat must be calling for heat.

OK, I have done this. Pilot light was lit, picked up jumper put it on 2 and 4, burner lit, then went out.
If this helps at all, I figured out the whole pilot adjustment screw, I just needed to turn it a lot more than I was. It also seemed to make the burners burn hotter or colder. If I had it all the was on high, the burners would only light for a split second. But if I turned it way down, the burners would stay lit for 2 or 3 seconds.

If we are indeed talking about a white-rodgers flame sensor, you can test the valve by: unplug the flame sensor..install a jumper in holes 3 & 4..pilot should light....now take the jumper and install in 2 & 4..main burner should come on..remember thermostat must be calling for heat.


This is interesting. Something I have not run across or had to do yet.

You mean that if you only use one jumper set and you disconnect it to then use it to put it on 2 & 4, the main burners will come on? You'd think by disconnecting it from pilot terminals that the furnace would shut down on safety mode.

So are you sure about your test procedure? Sure it does not require a jumper left on pilot jumper terminals where then, once the pilot is lit you also add a second jumper set to the main terminals to keep it going? Or, do you have to transfer the jumper extremely quickly between terminal 3 and 2?, while leaving the other end on 4?

Obviously the poster needs confirmed accurate information because he does not want to waste $80.

OK, I have done this. Pilot light was lit, picked up jumper put it on 2 and 4, burner lit, then went out.
Do you hear the gas valve clicking off when the burners goes out? Take a meter to be sure you are getting 24 volts the whole time of 24 volts is there the whole time, I am going to point to a weak gas valve that won't hold open.

This is interesting. Something I have not run across or had to do yet.

You mean that if you only use one jumper set and you disconnect it to then use it to put it on 2 & 4, the main burners will come on? You'd think by disconnecting it from pilot terminals that the furnace would shut down on safety mode.

So are you sure about your test procedure? Sure it does not require a jumper left on pilot jumper terminals where then, once the pilot is lit you also add a second jumper set to the main terminals to keep it going? Or, do you have to transfer the jumper extremely quickly between terminal 3 and 2?, while leaving the other end on 4?

Obviously the poster needs confirmed accurate information because he does not want to waste $80.


I am positive about the procedure. If pilot goes out when jumper is removed the valve needs to be replaced. The valve should have stayed on when the 2 & 4 holes were jumped. I hope he didn't remove the jumper and expect the burner to stay on. This procedure is mimicing the flame switch function.

I am positive about the procedure. If pilot goes out when jumper is removed the valve needs to be replaced. The valve should have stayed on when the 2 & 4 holes were jumped. I hope he didn't remove the jumper and expect the burner to stay on. This procedure is mimicing the flame switch function.

I only used one jumper. And by jumper I mean I nail I bent to fit... The pilot light stayed lit while I moved it to the burner switch.