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Problem: Why is the pilot light on my furnace going out after a new roof installation?

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Problem: The pilot on my furnace will not stay lit after we had a new roof installed.  The only changes I’ve made are: New cheap $1.58 furnace filter (30-day) Ace Hardware, New roof, and New roof vents (my attic is SO windy compared to before) Maybe the roofers disconnected the furnace vent in the attic and it’s causing a back-draft? Thanks greatly for any help. I’m very desperate! Lori

Answer:  Hi Lori! There are many reasons that could cause a pilot to not stay lit. One reason could be a bad thermocouple or gas valve. We discuss this problem with the thermocouple in a post we have on the following page: We have a YouTube video below made by Luke Stafford that explains how to change a gas thermocouple. Other things to check would be, since you had a new roof installed are:

1. Many times the roofers knock, sand off the shingles, dirt, or rust onto the burners or into the pilot light, and the pilot and burners need to be cleaned to work and burn properly. You should have a nice blue flame that encompasses the thermocouple. If the flame is not blue or not strong you probably need to clean the pilot. If the pilot is yellow the pilot needs to be cleaned.
2. Rust or dirt that falls on the burners can cause delayed ignition which would be like a mini-explosion when the furnace tries to light. This could cause the pilot to blow out when the furnace ignites. This usually happens when the furnace tries to light after it has been off for a while (the furnace is cold).
3. Check the furnace when the burners are on and make sure they are fully burning a blue flame from the front to back all the way. If not then the burners might need cleaning, the vent could be stopped up or if not burning properly only when the blower is on then this would be a sign of a heat exchanger leak.
4. Check to make sure that the hot gas is all going up your vent stack through the roof by feeling around the bonnet where the vent attaches to the furnace. If any heat is coming out around the bonnet when the gas is burning on your furnace then your furnace is not venting properly and you need to turn it off because this can be dangerous. Need to get the vent fixed.
5. The furnace and water heater vent as you know should run a couple of feet above the roof and not terminate in the attic. This is dangerous if it vents up in your attic. I could cause a fire or allow carbon monoxide into your home.
I hope this gives you some things to look for. I hope you can easily and inexpensively find and fix the problem. I hope that all the furnace needs is a good cleaning. Thanks for asking this question!

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2 thoughts on “Problem: Why is the pilot light on my furnace going out after a new roof installation?

  1. Hi,

    I have a ATH furnace that cycles on and off. Flames come on and off within a couple of seconds. Changed Flame sensor, nothing. Changed pressure switch nothing. Changed flame roll out sensor, nothing. Changed batteries in thermostat, nothing. Set thermostat to highest it can get to , nothing. The flue is good, air is going out and no blockage. If anyone has any suggestions please let me know before I take a sledge hammer to the thing! Thanks in advance for any help

    1. Please make sure all ground wires and connections are tight. I would suggest that you read the post on the following page and watch the videos. I hope they will help you find and fix the problem: Steve

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