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Edward
Edward, Handyman
Category: Home Improvement
Satisfied Customers: 7966
Experience:  Handyman, Master Gardener
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My furnace turns on then shuts off. What is the problem?

Customer Question

When I flip the switch on my Colman Evcon unit, sometimes it will come on and heat for 2 to 5 minutes and then shut off. Other times the unit will act as if it’s trying to turn on and then shut right off. This can go on two or three times in a row. Then it will sit quite for 30 minutes to an hour. Then try to kick back on. I have watched the idiot light on the unit and it blinks at a steady bright/dim indicating all is normal. I have tried replacing the thermostat and that did nothing. I have also jumped the red and white wires together to see if it will run continuously and it does not. I had what I believe is called the vacuum switch or valve? I am stumped to what the problem might be?

Submitted: 8 years ago.
Category: Home Improvement
Expert:  Edward replied 8 years ago.

Hello,

Thank you for asking your question on Just Answer.

Could you explain your situation a little more?

What is the make and model number of the furnace?
When was the last time the furnace was professionally serviced?
What is the age of the furnace?
What fuel does the furnace use?
What have you tried to correct the problem?
Do you have a digital camera that you could use to send pictures of the furnace if needed?
Thank you again for trusting us with your problem.

Please reply as soon as possible so that we can finish answering your question.

Customer: replied 8 years ago.

The unit is a Colman Evcon, Model BGM08012CX, SN 9 4 0 3 2 9 0 0 9. The age is 14 years old. It runs on natural gas. The unit was last serviced about 5 years ago.
In my original e-mail I mentioned what I have done to correct the problem.
I do have a camera and I can take a photo of the area you would like to have the photo taken.
Thanks

Expert:  Edward replied 8 years ago.

The first thing I would suggest checking is the flame sensor. It will cause the problems you have described. The flame sensor can be cleaned with a wire brush or sandpaper. The flame sensor very seldom becomes defective, unless their ceramic base cracks. Check the base for cracks while cleaning the flame sensor and replace the sensor if the base is cracked. This problem can also be caused by lack of cleaning the furnace and having the burners cleaned.

Many homeowners do not realize, the complications of not having a professional inspect the heating system yearly, can cause. If a fire, or worse, is caused by the furnace and there are no records of the furnace being maintained, the insurance company can and will deny the claim for damages. I have worked on systems after they have caught fire and the homeowners got no help from their homeowners insurance for the damage. I have installed furnaces in new homes that the owners were building to replace a home that was destroyed by fire from not having the furnace serviced. I like every customer to have this information to consider before repairing the furnace themselves.

Should you require further clarification, never hesitate to ask. It would be my pleasure to clarify my answer to your question. If after reviewing the above information, you have additional questions, I will be glad to answer them. My goal is your 100% satisfaction with all questions I answer.
Regards

Customer: replied 8 years ago.

When I had the heating guy out to check the furnace, he said the unit looked really good and he cleaned out any build up he could find.
He first said it might be the sensor panel??? He said an easier replacement and cheaper item that also could cause the problem is vacuum valve, he was able to run the burners at full blast and they ran until he shut them off. This had something to do with a connection he made inside the furnace box.
So I question the flame sensor. Is this normal on a Colman and have you worked specifically with these units?
Thanks for your feedback.

Expert:  Edward replied 8 years ago.

Yes the flame sensor is a common part on all gas furnaces unless they are a very old model. Yes, I have worked on many Coleman Furnaces and assisted several customers with repairing their units. Click here for information about the flame sensor.

Should you require further clarification, never hesitate to ask. It would be my pleasure to clarify my answer to your question. If after reviewing the above information, you have additional questions, I will be glad to answer them. My goal is your 100% satisfaction with all questions I answer.
Regards

Customer: replied 8 years ago.

Sorry for the delay. I just got off the phone with the heating guy who has been working to fix my furnace. I wanted to find out first if he had checked the flame sensor. He said it was the first thing he checked, he pulled it out, cleaned it off and there were no cracks.
The way the furnace acts, is when you turn on the furnace from the thermostat, you hear the electronic inducer engages and then it shuts off before the flame sensor picks up. This can happen 2 or 4 times before the system fires and you hear the burners running at full force. However that becomes short lived. It may run for 2, 3 maybe even 5 minutes and then shuts off. If you turn the thermostat off and back on, it's as if it resets the system and the process starts over.
Any thoughts?

Thanks

Expert:  Edward replied 8 years ago.

Thanks for the reply and the additional information. The draft inducer (electronic inducer) has a tube connected to it that goes to the pressure switch. The pressure switch checks for the correct air flow in the duct. After the pressure switch stops the furnace from operating 3 times it will cause the lights to flash and the furnace will have to reset to try again.

The tube that connects the draft inducer to the pressure switch can get dirt in it. This will cause the pressure switch to shut the furnace down. The ports that the hose connects to can get stuff in them also. This can be cleaned out using a small wire. Do not blow into the pressure switch or it will be damaged and will need to be replaced.

Other things that can cause a problem with the pressure switch shutting down are dirty filters, an A coil that needs to be cleaned, any blocked return air vents, dirt on the draft inducer blower blade, dirt on the furnace blower blade and a obstruction in the chimney that would keep the chimney from getting a good draft.

I believe one of these are causing the problems you are having.

Should you require further clarification, never hesitate to ask. It would be my pleasure to clarify my answer to your question. If after reviewing the above information, you have additional questions, I will be glad to answer them. My goal is your 100% satisfaction with all questions I answer.

Regards

Customer: replied 8 years ago.

We have replaced the pressure switch already, so I know we are good there. This was the least expensive item to replace so we tried it first. What about the master switch board (not sure what it is actually called) the box on the unit that has the idiot light on it that blinks to tell you how the system is working? This was also suggested as an item that might be causing the problem. As I mentioned in one of my earlier responses, this light never changes from a normal bright/dim blink.
Thanks

Expert:  Edward replied 8 years ago.

You have done a very good job at providing the information and trying to correct the problem. The main board of the furnace is expensive and to continue to replace the parts that are not known to be the problem will get very expensive fast. The only suggestion I have left is to have a professional that can be there to diagnose the problem, diagnose and repair the furnace.

Regards