Furnace questions...

[steved]

OK, blew the cobwebs out of my DuoTherm this past weekend... it will now work for a while...

After it works for a while, the pilot starts to flicker (like it is blowing out), then will extinguish. I was thinking bad propane initially, now I'm thinking bad thermocoupler?? It acts like it is shutting the gas off... I have adjusted the pilot down so it didn't "cook" the coupler, and still have problems.

Oh, and if you leave the trap door off, it will stay on longer than with the door closed... and I know its not air because the main burner works fine with the trap door closed.

Anyone else have these symptoms? I have more/less figured it is the thermocoupler or the valve itself...

 

[jelag]

The reduction of temp on the thermocoupler might be your problem... the end of the thermocoupler needs to be in the flame or the tip of the flame for it to function correctly...

The theory of operation is that as the bulb heats at the end of the thermocouple the expansion will keep the valve open to the pilot... also some heaters have a deflector to keep any air that flows in the area from blowing the tip of the flame in the wrong direction and allowing the heat to go somewhere besides on the bulb... .

Hope this helps...

 

[steved]

The reduction of temp on the thermocoupler might be your problem... the end of the thermocoupler needs to be in the flame or the tip of the flame for it to function correctly...



The theory of operation is that as the bulb heats at the end of the thermocouple the expansion will keep the valve open to the pilot... also some heaters have a deflector to keep any air that flows in the area from blowing the tip of the flame in the wrong direction and allowing the heat to go somewhere besides on the bulb... .



Hope this helps...

OK, but doesn't the thermocoupler also shut off the gas if it gets too hot?



The flame looks identical to my old furnace... in fact, everything looks identical to my old furnace, just that this one won't stay lit...

 

[WestTN]

The thermocouple generates a voltage that holds the gas valve open. Readjust the pilot flame to original and it will work fine.

 

[jelag]

The thermocouple will not turn off the gas if it gets too hot... it is looking for the heat of the pilot to keep the pilot running... there should be another over heat limit device in the electrical circuit of the furnace..... this over heat limit would shut down the furnace if the blower were to fail or not get the heat out of the furnace fast enough... or excessive gas pressure and it overheats... .

Dennis is right... . but remember that other thermocouples are mechanical devices and not electrical...

 

[RVTRKN]

steved: You have a PM with a phone number for help. I'm a certified tech. /instructor and contractor in HVAC and have an account with Dometic and can help. It will help if you have a camera phone and send a pic of the furnace and give me the model and serial number.



Steve...

 

[steved]

The thermocouple will not turn off the gas if it gets too hot... it is looking for the heat of the pilot to keep the pilot running... there should be another over heat limit device in the electrical circuit of the furnace..... this over heat limit would shut down the furnace if the blower were to fail or not get the heat out of the furnace fast enough... or excessive gas pressure and it overheats... .



Dennis is right... . but remember that other thermocouples are mechanical devices and not electrical...

OK, I thought they worked both ways. I'm pretty sure this one is a mechanical version, copper tube and all.



I've adjusted the flame up, adjusted the flame down, it just acts like it runs out of gas (literally). The flame will start dancing, the base will disappear (only the tips will be present), then it will finally "blow out".



Now that I'm saying this, the tips burning alone almost indicate the air-fuel mixture is wrong?



RVTRKN: It'll be a few weeks before I can get back to it... leave for Washington tomorrow.

 

[jelag]

RVTRKN

Would you give me an overview of the Dometic 2 door fridge recall. . My 5er wasn't in the first group but is now in the second group...

Whats involved and the time to tie up the 5er...

Thanks

 

[HPetrat]

If the unit has been sitting for a while, and exposed to weather, you may have an issue with moisture in the piping.



I have had similar issues on several friends RV's and found that turning on all of the gas appliances on a "high" setting for about an hour usually clears the moisture out of the system. On one occassion I did have to purge the lines to dry and clear them with an inert gas.



Just my experiance,



HP

 

[RVTRKN]

RVTRKN



Would you give me an overview of the Dometic 2 door fridge recall. . My 5er wasn't in the first group but is now in the second group...



Whats involved and the time to tie up the 5er...



Thanks

Sorry jelag, I have no info for you except what you have more than likely read on their web site at Dometic USA. There you will get a phone number you can call and have your model and serial numbers ready. I just now got involved with them when I replaced my AC on my 5ver, and I repaired my own furnace awhile back but paid too much for the part. The controls are the same as reg. furnaces but 12VDC on most parts. My system used flame rectifacation with an ignitor for proving and lighting the pilot. The reason I PM'ed steved and not explain it on the thread, is it probably is flame rectifacation that he has. With me being a HVAC contractor I was able to get a wholesale account with them.

 

[pgleavitt]

Thanks for the mention to the fridge recall. I just purchased a used 2003 RV and found that I'm included in the recall.