Please diagnose my fireplace problem

[RCJH]

My 3-year old Mendota FV44i fireplace won’t stay on, and I think if I describe the symptoms, you can easily diagnose the problem (we use LP gas). A few months ago I turned on the fireplace using the remote. The pilot light came on, and a few seconds later the burners came on, but the flames were blue. That lasted for about 10 seconds, and then the burners and the pilot went out. I turned it off, waited a few seconds, and then turned it on again. The same thing happened, only the flames started to get a little yellow. I repeated this process 3-4 times before the fireplace would stay on. This continued for several more weeks, although it kept taking more attempts to get the fireplace to stay on, until one day after about 8 attempts I gave up. I even waited longer each time after the flames went out, up to 3 minutes, before I would try again. Then I accidentally stumbled on a solution that seemed to work. I normally keep the pilot light off, but this time I turned the pilot to continuous on mode and waited 5 minutes before I turned on the fireplace. This time it worked - the burner flames started out blue, but eventually turned their normal yellow color and I ran the fireplace for about an hour. Since I don’t like to have the pilot on all the time, after I turned off the fireplace I turned the pilot back to intermittent. The next day I tried again, but I only kept the pilot on for about 3 minutes before I turned on the fireplace - it failed. And once it fails, I have to wait up to several more minutes before I can get the pilot started again. I hope that’s enough information for someone to identify the problem. I suspect it's just a bad thermocouple, and I probably won’t fix it myself, but I’d still like to know what the problem is before I call the service department.

 

[DAKSY]

Your symptoms might indicate a venting issue. Have you tried lighting the unit with the glass front partially opened? If so, does it continue to burn normally?

 

[RCJH]

Thanks so much for your quick reply! I'm not exactly sure what you mean about a venting issue, and I should have provided more details. This is a gas insert that went inside an existing wood-burning fireplace. It is a direct-vent system that was routed up through the existing chimney. So there really isn't a glass front to open unless you're suggesting that I remove the door. Is that what you mean? In any case, if it was venting problem, why could I sometimes get it to work?

 

[Lennox65]

If it starts and runs correctly in "Continuous Pilot" Mode, then you probably have Cold Chimney Syndrome.

 

[DAKSY]

If your direct vent unit can’t get enough combustion air, the pilot & burner flames will extinguish. When the burner is lit, the evacuation of exhaust gasses causes the intake of combustion air. If there is a restriction in the intake - like a beehive - symptoms similar to yours can occur. If you remove the door -only for a short period of time - & the flames burn properly, that may determine if the venting is the issue. You said in your original post that in continuous pilot mode it worked fine. That would tend to indicate that the thermocouple is functioning correctly. Have you had the unit serviced since you’ve owned it? It should be checked every year or so

 

[RCJH]

If it starts and runs correctly in "Continuous Pilot" Mode, then you probably have Cold Chimney Syndrome.

Thanks for your suggestion. I had to look up "Cold Chimney Syndrome" (aka Cold Hearth Syndrome), and after reading about it, I don't think that's the problem or it would have happened all the time over the past 3 years, winter and summer. This is a recent development. Until about 3 months ago the pilot was always set to intermittent mode, and the pilot and burners would start up on the first attempt with no problem all year round. We also live next to the water on the Olympic Peninsula in Washington, so we have mild winters (rarely gets below 30) and mild summers with a slight chill in the air on some mornings. I could be mistaken though - I'll have to wait for cooler weather in the fall to do some more thorough testing.

 

[Fingerlakes Fireplace]

Thanks for your suggestion. I had to look up "Cold Chimney Syndrome" (aka Cold Hearth Syndrome), and after reading about it, I don't think that's the problem or it would have happened all the time over the past 3 years, winter and summer. This is a recent development. Until about 3 months ago the pilot was always set to intermittent mode, and the pilot and burners would start up on the first attempt with no problem all year round. We also live next to the water on the Olympic Peninsula in Washington, so we have mild winters (rarely gets below 30) and mild summers with a slight chill in the air on some mornings. I could be mistaken though - I'll have to wait for cooler weather in the fall to do some more thorough testing.

Its a venting problem. When the fireplace and pilot are off, everything is cold and you have no "draw". When you start the fireplace, it will burn up all the oxygen that is in the firebox , and then die out.
BTW your fireplace does not have a thermocouple or thermopile.

 

[RCJH]

Its a venting problem. When the fireplace and pilot are off, everything is cold and you have no "draw". When you start the fireplace, it will burn up all the oxygen that is in the firebox , and then die out.
BTW your fireplace does not have a thermocouple or thermopile.

Thanks for your explanation. You are correct about the thermocouple and thermopile, and after looking at the parts list, I realize that my fireplace doesn't have those. I'm still totally confused about the venting problem diagnosis, but you are now the third person who says that's the problem, although it still doesn't explain why the fireplace and venting system worked fine for 3 years and now it suddenly has a venting problem. I could understand if something got into the vent and is blocking the airflow, but then why does it work if I just let the pilot run for 10 minutes before turning on the burner (I have never had to do that before either). Nevertheless, I'm going to remove the glass front, try to start it, and see what happens.

 

[RCJH]

Thanks for your explanation. You are correct about the thermocouple and thermopile, and after looking at the parts list, I realize that my fireplace doesn't have those. I'm still totally confused about the venting problem diagnosis, but you are now the third person who says that's the problem, although it still doesn't explain why the fireplace and venting system worked fine for 3 years and now it suddenly has a venting problem. I could understand if something got into the vent and is blocking the airflow, but then why does it work if I just let the pilot run for 10 minutes before turning on the burner (I have never had to do that before either). Nevertheless, I'm going to remove the glass front, try to start it, and see what happens.

Your symptoms might indicate a venting issue. Have you tried lighting the unit with the glass front partially opened? If so, does it continue to burn normally?

 

[RCJH]

To Lennox65, Daksy, and Fingerlakes Fireplace: You were all correct... it must be a venting problem because it seems to work fine with the glass front partially open. I still don't understand what changed, and why it works if I just let the pilot run for 10 minutes first before turning on the burners. However, if something is blocking the intake air (like a bee hive), it's beyond my ability to fix because I'm too chicken to climb up and peek inside the chimney on top of our 3-story house. The company made a return visit after they installed the fireplace to put bird spikes around the vent - a Northern Flicker (woodpecker) was driving us crazy hammering on that thing - it sounded like amplified machine gun fire coming through the fireplace. I got up there once to take this photo a few years ago and my pucker factor was off the charts!

 

[49er]

Wow, what a beautiful spot for your home! You're right about the pucker factor though, I'm nervous about getting on our single story roof anymore.