furnace cycles continuously

[thelightners]

2001 Thor Wanderer with Surburban 30F furnace.
The fan comes on, the igniter clicks, the flame lights, the flame goes out.
Repeat cycle.
About one ti.me in ten the flame will stay on.
It seems that the thermostat, limit switch, the sail switch, controler board, spark electrode, gas valve are all ok.
I've searched the boards, but nothing I've found there seems to cause the symptoms I'm having.
Any help greatly appriciated!

 

[Karl]

Could be the thermocouple; that thin brass tube that is supposed to stick in or very near the flame. Sometimes it gets moved and won't sense the flame. How long does it stay lit? A couple seconds?

Let me modify this a little. There are two types of flame sensors - one, the thermocouple and two, an electrical wire that senses the passing of electricity through the flame. You'll have one or the other; not both. 

 

[thelightners]

Thermocouple tests ok.  I suspected the propane regulator, so I decided to put in the spare.  When I took the old one off, about a half an ounce of what looked like new motor oil came out of the low pressure side of the regulator.  I am guessing that this is the cause of the furnaces problems.  Any idea of what this might be or how it got in to the regulator?  I don't want to foul the new regulator if this stuff is in the propane bottle.  The main gas line had quite a bit of this gunk in it so I replaced it. Fortunately it hasn't made it as far as the appliances.  Can the bottles be cleaned out?

 

[Shayne]

Never heard of oil in the propane tanks and never heard of 1 being cleaned.  Sounds more like flame adjustment with wet propane mixing with the soot from the combustion area forming the oil like feature.  The flame should be blue once it ignites, and probably had a yellow flame.   JMHO

 

[thelightners]

If that were the case, how would the gunk migrate upstream to the regulator (about 20 feet)?  There is no trace of it in the supply line that runs from the main line to the heater, despite the fact that when I removed the main line quite a lot of it drained out.
It is a clear amber fluid, with no apparent particulate matter suspended in it.  It's viscosity seems similar to 5W20 oil, and it is oily to the touch.  It is not water soluble, but cleans easily with Ivory soap and water.
Could this be a lubricating fluid that is leaking past the seals of the pump where I have been having my tanks filled lately? 
Help!

 

[Shayne]

Have you discussed this with them (Where You Fill your Tank.)?  I had My mind thinking something else on previouse statement.  I was thinking it was all at the furnace itself.  Reread and saw I misread.

 

[Gary RV_Wizard]

Yes, that was the problem. A furnace uses a relatively huge amount of propane, so it will fail while the stove or water heater may still function. It's not oil per se, but that's a common description for it.

There are various additives and impurities in propane that can accumulate over time and moisture from condensation can also accumulate in the tank. These combine into oily globs, much like when oil spills in the ocean. It generally settles in the bottom but once in awhile (perhaps while in motion?) some of this gunk can get sucked into the outlet tube. It will clog the orifice in a regulator and also the jets in the burner if it gets that far.

It's probably not worthwhile to try to clean the regulator - the diaphragm is probably soaked with the stuff. Toss it out - they aren't that expensive.  There may be more in the lines up or downstream from the regulator - the common technique is to open both ends of the lines and blow the them out, back towards the tank. Do not blow the lines with them still connected to any appliance - you could blow gunk into the burner tubes and mess them up too.  You might gamble on the tank and not get it cleaned.  I don't know how expensive that would be, but you have to drain it and it maybe has to be removed (?). Then remove the valve and OPD device to get into the tank proper for cleaning. I suppose and LP shop could give you  an estimate. I would probably gamble another regulator and see if the problem re-occurs.

 

[thelightners]

Thank you for your detailed response.  I can feel confident now that the repairs are now finally complete, after a week of head scratching and bewilderment. Is there a way to prevent this kind of build up?  This could have been a very serious situation if it had happened last winter when we were in Edmonton, Canada!