Surburban furnace problem

flirtypup · 11-15-2010, 11:01 PM

OK heater wont stay lit. But If I put tape over the cold air intake on the outside of my unit it works flawless. Remove the tape heater goes out instantly. And ideas? Its not power supply, not low gas pressure. Its something with airflow. There are no mud dubber nest inside the tubes that i can see.

**Herk7769** · 11-16-2010, 08:57 AM

Try to see if this can help:

**Bama Rambler** · 11-16-2010, 09:48 AM

Are you completely covering the intake or just partially? sounds like a mixing chamber adjustment problem. Possibly from a spider building a web inside the burner throat.

**Herk7769** · 11-16-2010, 03:02 PM

Or a "stink bug" cacoon, They are very tightly woven.

flirtypup · 11-16-2010, 07:11 PM

OK I pulled the unit completely out. There s nothing inside . not even a trace of insects. Took my craftsman yard blower . ( just happens the nozzle matched ) Blew from the intake side for 2 minutes then the exhust side . Nothing came out. Reinstalled. Hit the switch wont lite. Reset covered 2 of the 3 intake holes she lite up and ran wonderful.Remove the tape goes out again.
Seriously considering electric insert and 50 amp service.

**Herk7769** · 11-16-2010, 07:27 PM

Look on page six of the troubleshooting manual.

In my opinion, your problem might be the "Flame Sense" circuit on the main board is bad.

It works by looking for ions in the air flow from the flame being lit. No flame, no or "not enough" ions in the air. With normal air flow to the burner the sensor may not be seeing "enough" ions to convince the main board that the fire is lit and shuts down the furnace.

Blocking some of the incoming air might allow more ions to concentrate at the sensor and the main board then is happy and allows the flame to keep going.

This company carries circuit boards for most of our products that use them. Dinosaur Electronics Home. High quality circuit boards for RV appliances.

**Bama Rambler** · 11-17-2010, 08:32 AM

I think I'm confused. Are you covering the combustion air intake on the outside of the RV or are you covering some of the return air holes on the inside of the RV but the outside of the furnace?

**Herk7769** · 11-17-2010, 09:13 AM

"Cold air intake on the outside of my unit" I took to mean the combustion air intake.

Since the Combustion air fan and the Blower air fan are on a common shaft motor, I can only assume that restricting the airflow to the burner allows the flame to light and stay lit.

That could be a problem with the flame sensor not detecting the fire that is there or a too lean mixture setting that needs much less air to stay lit.
Since it worked before, and he did not indicate he changed any settings (if the air feed tube was restricted you would have an over rich mixture not a lean one) I am leaning toward a bad board.

**Bama Rambler** · 11-17-2010, 09:55 AM

["Cold air intake on the outside of my unit" I took to mean the combustion air intake.]

I did too at first but then he said,

"Reset covered 2 of the 3 intake holes...."

Since all the units I've seen have only one intake hole for the combustion air inlet and multiple holes for the return air, it gave me pause to think.

**Herk7769** · 11-17-2010, 11:10 AM

The intake hole has a tripod shaped support. I assumed he meant he covered two of the three triangular shaped inlets in the round inlet pipe.

I could be very wrong though. Flirtypup needs to clarify.

flirtypup · 11-17-2010, 05:56 PM

Here s a picture if I can make this work

Our website - Mouton News
I hope this link works . The 1st pictire it will not lite. the second picture with me covering 2 holes it works like a champ.

**Herk7769** · 11-17-2010, 06:18 PM

That's what I thought, Flirty. Thanks for the photo to confirm it though.
If you are sure there is plenty of heat with the inlet blocked (there is a possibility that the propane valve itself is not opening fully), I would be looking at the main board.

I am not a repair dude, I try to figure out the most likely fault; then pull the LRU (Line Replaceable Unit); and replace it.
See if that fixed the problem.

A certified technicial would figure it out immediately and fix it. It would most likely cost more if you both guessed right, but would be a lot less if you guessed wrong.

(Don't Ask Me How I Know - DAMHIK)

flirtypup · 11-17-2010, 07:52 PM

Yes , I think I've gone as far as I feel safe going with this. After all I'l be sleeping with this thing running. I think I'm going to bring it to a certified shop and let them do it rite. Thanks for all the help. this has just goten a little to critical for me to mess with.

**Herk7769** · 11-17-2010, 08:03 PM

There is an aviation story about this very topic.

The Air Force spends several hundred thousand dollars to train pilots how to fly in instrument conditions. The reason they do that is NOT so they CAN fly when the weather's bad, but to know WHEN NOT to fly when the weather's bad.

Clint Eastwood said it pretty good too.

"A man has GOT to know his limitations."

**Bama Rambler** · 11-18-2010, 08:35 AM

Thanks for the pics. That cleared it up and there are several things that could cause the issue you're seeing. Low gas pressure is one, bad gas valve is another, and a few more. At this point I think you're wise to call in a pro. They'll have the knowledge and tools to figure it out.

flirtypup · 11-20-2010, 04:34 PM

OK Can close this down now . Brought it to the dealer. He flipped the switch and it works. He says nothing wrong with it. Everthing in normal operating range. His best guess maybe when I put the leaf blower to it , that clear it out.

**Herk7769** · 11-20-2010, 04:45 PM

Well there you go!

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