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My comfortmaker furnace won't stay running. The flame comes on but it looks like the main flame is not going into the burner tube very well. The flame seems to be outside of the tube and there is a high limit switch on each side of the burner box. They are wired in series. The left side gets very hot (because the flame is not going all the way into the tube) and opens up (checked it with my volt meter). I am a electrician (licensed) and also a maintenance millwright so hopefully I have given a good explanation to what is going on. The model is a FBF100F14G1 natural gas furnace. The two limit switches that I am referring to are called "roll out switches" there is one on each side of the burner. I turned the gas pressure down on the main regulator until the flame stayed away from the switch and more inside the burner tube. I am not saying or satisfied that this is a fix. It is temporary. The furnace is runnig and working now.

Submitted: 20 days and 4 hours ago.

Category: HVAC

Value: $15

Status: CLOSED

Make : Comfortmaker
Model : FBF100F14G1

Already Tried:
I have checked everything I know of and it seems to be the left high temp switch in front of the heater box is getting hot and opening and shut off the burner.

Posted by Billy 20 days and 2 hours ago.

Info Request

does the burner run decent before the blower kicks on?

20 days and 2 hours ago.

Reply

I will have to check that I am not sure. I can start the furnace again and see.

Posted by Billy 20 days and 2 hours ago.

Info Request

Here is what we need....there is either a blockage pressurizing the cell or a crack or hole allowing the blower to enter the combustion chamber. I need to know if it does it right away orafter main blower

20 days and 2 hours ago.

Reply

The flame kind of fluffs out of the burners. Especially on the left side. It does this before the supply/circulating fan runs. Only the draft inducer is running. I turned the pressure down to the manifold to keep the rollout switch from getting too hot and kicking out but it seems like there is not enough draft to pull the flame fully into the burner tube.

Posted by Billy 20 days and 2 hours ago.

Answer

ok, you will need to pull the draft motor and face plate. Odds are you have a plugged cell at the narrow passages at the transitions. Decreasing the pressure will most likely cause a sooting issue eventually and lead to more blockage. This is a good 2-3 hour job and requires removing most of the face and having a shop vac ready.

20 days and 2 hours ago.

Reply

I see, you are thinking the top of the burner cell is plugged and the draft inducer cannot pull a draft thru and pull the flame into the burner.

Posted by Billy 20 days and 2 hours ago.

Info Request

That is correct. I am assuming the rust flakes and residueare plugging the upper portion of the exchanger. Pretty common, inducer sucks from path of least resistancde so the other burners get all the draft.

20 days and 2 hours ago.

Reply

One more thing before I accept and leave your assistance. I did turn down the pressure to the manifold on the main regulator. The furnace is burning ok, no yellow. I would like to leave this for today and come back tomorrow and tear this apart for my friend. Is that ok? You don't think this could be a plugged chimney pipe by chance or are you pretty sure it's the exchanger? Thank You,

Posted by Billy 20 days and 2 hours ago.

Answer

If it were plugged chimney the draft pressure switch would not make. The one good thing about this furnace is if flamegoes anywhere it is not supposed to, or if pressure switch fails , or unit overheats...it just shuts down.

I cannot advocate any changes outside of manufacturers recommendations. I know you would like the old "it will be ok".....but I am not in a situation where I can give that type of response sight unseen.

20 days and 2 hours ago.

Reply

I understand. I am a licensed electrical contractor and I totally can understand why you cannot give the ok for the pressure adjustment. I appreciate your help Billy. Thank You.

Accepted Answer

You are very welcome and I am glad you understand. Thank you.

Accepts:
Expert:	Billy
Pos. Feedback:	99.7 %
Answered:	11/3/2009

HVAC Mechanic

State Licensed Mechanical Contractor, Heating, Cooling, Oil Burners, Heat Pumps, Boilers, Geothermal

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Optional Information

Make : Comfortmaker
Model : FBF100F14G1

Already Tried:
I have checked everything I know of and it seems to be the left high temp switch in front of the heater box is getting hot and opening and shut off the burner.

Info Request

does the burner run decent before the blower kicks on?

Reply

I will have to check that I am not sure. I can start the furnace again and see.

Info Request

Here is what we need....there is either a blockage pressurizing the cell or a crack or hole allowing the blower to enter the combustion chamber. I need to know if it does it right away orafter main blower

Reply

Answer

Reply

I see, you are thinking the top of the burner cell is plugged and the draft inducer cannot pull a draft thru and pull the flame into the burner.

Info Request

That is correct. I am assuming the rust flakes and residueare plugging the upper portion of the exchanger. Pretty common, inducer sucks from path of least resistancde so the other burners get all the draft.

Reply

Answer

Reply

I understand. I am a licensed electrical contractor and I totally can understand why you cannot give the ok for the pressure adjustment. I appreciate your help Billy. Thank You.

Accepted Answer

You are very welcome and I am glad you understand. Thank you.

HVAC

Have your own HVAC question?

Related Hvac Topics:

Question

Optional Information

Make : ComfortmakerModel : FBF100F14G1 Already Tried: I have checked everything I know of and it seems to be the left high temp switch in front of the heater box is getting hot and opening and shut off the burner.

Info Request

does the burner run decent before the blower kicks on?

Reply

I will have to check that I am not sure. I can start the furnace again and see.

Info Request

Here is what we need....there is either a blockage pressurizing the cell or a crack or hole allowing the blower to enter the combustion chamber. I need to know if it does it right away orafter main blower

Reply

Answer

Reply

I see, you are thinking the top of the burner cell is plugged and the draft inducer cannot pull a draft thru and pull the flame into the burner.

Info Request

That is correct. I am assuming the rust flakes and residueare plugging the upper portion of the exchanger. Pretty common, inducer sucks from path of least resistancde so the other burners get all the draft.

Reply

Answer

Reply

I understand. I am a licensed electrical contractor and I totally can understand why you cannot give the ok for the pressure adjustment. I appreciate your help Billy. Thank You.

Accepted Answer

You are very welcome and I am glad you understand. Thank you.

Related HVAC Questions

Make : Comfortmaker
Model : FBF100F14G1

Already Tried:
I have checked everything I know of and it seems to be the left high temp switch in front of the heater box is getting hot and opening and shut off the burner.