Direct vent burner shuts down

[mowildone]

I posted the other day about a problem with my thirteen year old LP direct vent fireplace.
The problem is/was that when the switch was turned on the gas tube would not keep flame.
I have not worked on it but tonight, on a hunch I flipped the switch on and the main burner ignited and continued to burn until I shut it down.
The only external difference is that the outside temperature moved from single digits to 40+ degrees.
Outside air is always available in the firebox. No damper. The box can get pretty cool.
Any thoughts?

Thanks

 

[jtp10181]

https://www.hearth.com/econtent/index.php/forums/viewthread/12577/

Why didn't you replay to the other post so people could see all the info?

Personally I would not really be messing around with an LP gas appliance myself. You should hire a professioanl fireplace repair person to come take a look at it. There are a lot of variables that can cause a unit to shut down by itself.

Is the unit B-Vent? That add extra reasons why it could shut down.

 

[mowildone]

Thanks for your reply.
I apologize for not doing a "replay" to my other posting.

I am new to this forum and 1. Not sure how to do a "replay". 2. Did not want to bury this new information in the old thread since it appeared to be inactive and 3. Thought, since the unit decided to return to life that this could be considered a new subject.

With regard to hiring a professional repair person, the unit is currently working and I am not sure what he will tell me about why it stopped working.
In my defense I am a retired person on a fixed income, a registered professional engineer and hate to waste money by hiring someone to tell me my unit is working.
Only bringing the engineer thing in to explain that the engineer in me seeks answers and understanding. I still enjoy learning. I am the kind of customer most repair people hate, you know, the one with all the questions s hanging over your shoulder.

The unit is a direct vent. It vents straight out the back through an exterior wall.
It has seal glass to the room and it does not use vertical piping to vent gases and bring in air.

FYI, A summary of the earlier post: The unit worked fine for thirteen plus years. About a week ago the burner flame would not sustain itself. Start up and flash off. The pilot light remained on and the thermogenerator was producing 450-500MV. When the switch was thrown, and the burner started to kick in, the voltage dropped to 150-200MV. As the main burner flashed, the pilot light flame slowly diminished almost to the point of going out.
I could not adjust the pilot flame. My thought was that the pilot orfice was restricted, reduced flame caused voltage to drop below the threshhold voltage at the main valve. I cleaned the orfice and thermogenerator. The unit fired up and all was fine until we had single digit temperatures. Then it stopped working again. I suspected LP tank regulation or feed line freeze. Not sure if line freeze is a possible. But now it is working and I was wondering why.

 

[Metal]

I would have to agree with jtp. Doesn't matter if you are a rocket scientist, propane is not something a do-it-yourselfer should try to tackle (IMHO). If you have the problem again call a pro. If you think you have a fixed income now, see what it looks like after your house is gone.

 

[jtp10181]

If the LP tank was low, a cold temp outside will reduce the vapor pressure. What you described with the burner coming on and pilot shrinking is exactly what would happen if the inlet pressure is low enough, all our fireplaces require at least 11" WC to function correctly with LP. Also if the unit has been running for 13 years with no parts replaced I would put in a new pilot assembly as well. LP tends to destroy thermocouples and thermopiles. They might just be getting weak. Often times we are replacing thermocouples every few years on LP units.

 

[Gooserider]

Idle thought - do you have any other gas appliances running off the same tank / line? Were they experiencing problems or operating normally? Perhaps some of the gas experts could comment, but I'd wonder if you had a combination of lowered gas pressure due to the cold, plus possibly competition with other appliances for a limited amount of gas - especially if they were "upstream" from the fireplace?

Gooserider

 

[mowildone]

Thanks for the replies.
The fireplace is the only gas device on this tank.

Still working great. Have not seen single digit temps since it started working again.
Checked voltage the other day.
Working great - Switch open 450MV, switch closed 225MV.
When it was not working - Switch open 450MV, switch closed 150-180MV.