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Edward
Edward, Handyman
Category: Home Improvement
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Experience:  Handyman, Master Gardener
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My gas furnace lights then shuts off after few seconds. Why?

Resolved Question:

My gas furnace lights then shuts off after few seconds. Why?

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

Hi,

Thank you for asking your question on Just Answer. The other Experts and I are working on your answer. By the way, it would help us to know:
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?

This problem can have several causes depending on the furnace that is in your home. The most common problem is a dirty flame sensor.Click here for information on the flame sensor. I can provide you more specific information when you have answered the above questions.

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.

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 sequence does not seem right. When it starts, both blowers come on and then the igniter then the burner lights. The first time it will run and produce heat, but when it cycles it won't stay on but the main blower will continue to run until it is manually shut down. It is a arcoaire rps II. The controller # is 50A50-112. There are 2 similar furnaces here. The other one works fine. The exhaust fan comes on then the burner will light and then the main blower comes on and stays on until the selected temp. is reached. It is a natural gas furnace.

Expert:  Edward replied 8 years ago.

The problem with the burner not staying lit is very likely as I had guessed a problem with a dirty flame sensor. Clean the sensor following the information in the link I provided and let me know if that corrects the problem. You may also have a problem with a sticking fan limit switch that will need to be replaced. This will cause the fan to continue to run.

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.

Customer: replied 8 years ago.

Would the flame sensor have anything to do with the fan sequence I described?

Expert:  Edward replied 8 years ago.

The main blower coming on and continuing to run until it is manually shut down is more than likely a fan limit problem. The burner lot staying lit is more than likely a dirty 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.

Customer: replied 8 years ago.

I switched the flame sensor with the other furnace and it is running ok. Please inform about the fan limit switch.

Thanks

Expert:  Edward replied 8 years ago.

Just clean the flame sensor you removed following the directions in the link and it should be fine. Click here for information on the fan limit control and here for fan limit switches.The limit switch will be connected to the heat exchange. If you have a digital camera that you can send an image of the inside of the furnace taken from the front of the furnace with the service door removed, I can likely point the part out to you.

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.

Edward and other Home Improvement Specialists are ready to help you