Problem with Coleman model #7956A856

[MKII]

This is my first post. Great forum! Well, my problem is that I woke up this morning to no heat! When I checked the pilot light, it was out. I had replaced the thermocoupler about 5-6 weeks go and it has been working fine. So I lit the pilot light again with no problem and it stays lit. When I turn the thermostat up to 70 degrees the furnace kicks on and blows heat for approx. 8-10 minutes (because it's only 50 degrees or so in here) and then all of a sudden it shuts off before the thermostat tells it to (not up to 70 degrees yet). When I check the pilot light, it's out again. The pilot light will light back up again with no problems. It seems as though the gas is somehow being shut off before it's supposed to be. Is the thermocoupler deffective in some way? Should I try a new thermocoupler? Any suggestions are greatly appreciated and thanks in advance for any help.

[hvac1000]

You may have a restricted pilot orifice which is being snuffed out when the burner shuts off. Clean the orifice first and make sure the t couple is in the flame at least 3/4 inch.

[MKII]

Thanks for the response. The pilot light will stay lit forever if I don't turn the thermostat up so that the furnace turns on. It seems like the burner and pilot are shutting off before the thermostat reaches what I set it to. The last time I lit the pilot and turned up thermostat today it ran for 20 minutes (while giving heat) and then the blower shut off and I don't think the thermostat clicked for it to go off. I checked the pilot and it was out again. I'm getting pretty frustrated right now. When you say to clean the orifice, are you talking about the end where the pilot is? Or the end inside the unit? I looked at the end where the pilot is and it's about 1/8th inch or so in diameter and looks open. The furnace has been working fine for the last 5-6 weeks so far.

[hvac1000]

If you follow the pilot aluminum gas tube you will see where it goes into the piloy itself. In the area where it connects to the pilot lite there is a orifice sized for the type of gas you use. natural or propane. The orifice has a very small hole in it to allow a small amount of gas to flow to the pilot so you can light it. This item (orifice needs to be cleaned ).

Careful do not make the hole any larger than it is now but make sure it is cleared out. This is the cheapest fix. if this does not work then it could be a bad heat exchanger or gas valve. Hopefully the orifice is plugged a bit or a small spider built a web in there.

[MKII]

I'm not exactly sure where this orifice is, but I will try to take another look at it. Thanks!

[MKII]

Okay, I followed the aluminum pilot gas line to the pilot light end, next to the business end of the thermocoupler. I don't know if I can explain this clearly, but all that I see is an approx. 1/2" X 1/2" deflector looking thing that's on an angle over top of the end of the pilot light gas line. It's connected to the end of the pilot light gas line like it's slid on, but it doesn't move. Then there's a hole about 1/8" in diameter. Is that the orifice or is it down inside the 1/8" hole? I can't see down into the 1/8" hole because the deflector thing is in the way. Do I have to take that end all apart to find the orifice? Sorry for being such a pain! Oh yeah, it's a gas furnace. Thanks!

[MKII]

Well, frustration has set in. I can't find the orifice to see if it's plugged and I can't get the end apart where I think it might be. Basically I'm not sure what I'm doing and don't want to end up with a bigger problem than what I already have! I'm going to have to let a pro fix it. Thanks for your help, much appreciated.

[MKII]

After trying to locate the pilot light orifice with no success and typing my last post last night, I put it all back together and re-lit the pilot and turned the thermostat to 70 for some heat. It ran for about 15-20 minutes and shut off. I figured that the pilot went out again, like it had been doing all day. About an hour and 15 minutes later, much to my surprise, the furnace kicked on again! The pilot didn't go out! It's still working fine this morning. I'm keeping my fingers crossed, but it looks like I accidentally fixed the problem while trying to find the pilot orifice. I have no idea what I did that fixed it?! Just dumb luck, I guess. Hopefully it keeps working. Knock on wood! Again, thanks for your help and suggestions.

[MKII]

Well, after three weeks of my furnace working fine since the last time I posted, I woke up this morning to no heat again! I got the pilot lit and it ran fine but the pilot light went out again when the furnace shut off. So I took it apart and tried to find the orifice again to clean it, but I don't think I found it. So I decided to just light the pilot and let the furnace run when I need heat until I can have a pro look at it tomorrow. But now when I light the pilot I can hear a noise like when the pilot is out on a burner on a gas stove. The noise sounds like a blowing or gas rushing sound. It didn't make that sound before when I lit the pilot. And now when I let go of the pilot button, the pilot won't stay lit. Why would the pilot light have that sound now when it didn't before? That sounds seems to be causing the pilot to not stay lit now. Thanks for any suggestions.

[Robert]

Hi,

Not sure w/o being there to test, but at this point, I think just letting Tech inspect is best for peace of mind and quick resolve of problem.



Thanks,
Robert

[MKII]

Thanks for the response Robert. I'm hoping that I can get someone over here tomorrow to look at it.

[Robert]

Hi,

You're very welcome, just not safe to guess on those type situations.


Without me doing hands on testing, it would be an educated guess and it's not worth it.



Thanks,
Robert