Furnace not lighting

[Curtisimo81]

Hey how is everyone doing today?  Ok so I tested my furnace before our camping trip on Friday because I knew it was going to get pretty cold this weekend.  The furnace worked just like it should.  At the campsite I went to turn it on and it wouldn't light.  The fan comes on, you can smell gas from the vent outside and hear the clicking for the automatic ignition.  But it would never light.  I switched bottles and ran stove for approximalty 5 mins then tried again.  Still wouldn't light.  Now I should add that it was trying to light.  I could hear the roar for a few seconds then it would stop.  I thought maybe bad regulator so I turned frig on gas, water heater, stove and oven then tried to turn it on again.  Still same thing.  The stove stayed lit and the flames never even faded a bit.  So I'm not thinking its my regulator.  Anybody have any thoughts? By the way both tanks were filled.  Thank you in advance for any help.  Oh yeah its a Hydro Flame 8525 Furnace. 

 

[Gary RV_Wizard]

If the burner actually lit and then went out, the timing is a critical clue. If the controller does not receive positive acknowledgment of the flame within several seconds, it will close the gas valve and shut down, requiring a reset (thermostat turned off & back on again is sufficient) to try again. This usually indicates a failed flame sensor (the sensor and the igniter are one and the same) or a corroded wire connection to it.

But if the flame literally went out on its own in 1-3 seconds, it sounds more like a gas supply problem. Could be the solenoid valve that feeds the furnace, or it could be a bit of dirt or oil in the gas line at that point (one that does not affect other appliances).

You may find this forum Library article helpful in understanding how the furnace works:
http://www.rvforum.net/miscfiles/Furnace_Trouble-2.pdf

 

[Curtisimo81]

Thanks for the advice. I have read the trouble shooting guide.  The thing that has me stomped is I smell propane bad from the exhaust so I know its getting propane.  I can also hear the clicking from the DSI, its just not lighting.  Im about ready to just pull the whole furnace out and take it apart to check for clogs.  My furnace is unfortunately located under the oven and no access panel to pull the front cover off.  There is an access panel under the stove but you cant see anything.  I just don't understand why it would work fine and now won't even light. 

 

[driftless shifter]

Is it colder than it was when it worked? Mine has been doing that. It is most likely a mercaptan stink oil slug in a propane line. The furnace uses more propane than any other appliance. you smell it and hear it but it can't sustain.
i took the cover off the furnace and aimed a 300 watt halogen work light at the furnace for about 20 minutes and it started working again. I have a mobile repair guy coming this Saturday to clean it up properly.

Bill

 

[Curtisimo81]

Is it colder than it was when it worked? Mine has been doing that. It is most likely a mercaptan stink oil slug in a propane line. The furnace uses more propane than any other appliance. you smell it and hear it but it can't sustain.
i took the cover off the furnace and aimed a 300 watt halogen work light at the furnace for about 20 minutes and it started working again. I have a mobile repair guy coming this Saturday to clean it up properly.

Bill

Yes it was about 30 degrees colder while we were camping. Maybe that is what is going on.  I took my furnace completely out this evening.  I plan on cleaning it out real well tomorrow and hopefully reinstalling it tomorrow.  If that doesn't work I might need to bring it somewhere.  Thanks

 

[Gary RV_Wizard]

Please be very exact about the symptoms, especially whether it lights even for a moment. At first you said it lit and quickly went out, and that is a significant clue (see my earlier response). But if it clicks and doesn't light at all, plus you smell propane, then that leads to a different conclusion, i.e. a blockage in the combustion air intake, or possibly the exhaust. Either one seriously disrupts the air/fuel mix and will prevent lighting, leading to the propane smell. Inadequate combustion air in particular does that. Spider webs, mud daubers, etc. in the intake or exhaust tubes are very likely causes.

 

[Curtisimo81]

At first it would come on for a few seconds then shut off.  The blower would still blow then it would relight and last a little longer each time until it stayed on. Once the coach reached the desired temp it shut off.  When it went to kick back on all it will do is the blower comes on you hear the clicking from the DSI but it will never light back up. Even if you turn the thermostat off and try again.  If you walk outside where the exhaust is you can smell propane coming out of exhaust and hear the DSI clicking but the furnace won't light back up.

 

[steveblonde]

Im not sure if this is helpful or not BUT on my furnace at home i have a small rod about 1/8 inch diameter and 4 inches long that sits over the burner, anyway it gets a carbon build up and need to be cleaned with an emery cloth - its a sensor of some sort . Regardless my home furnace does the same thing and i clean it with the emery cloth and im good for a couple years. Not sure if this helps

 

[bigbob70]

Curtis..

My RV furnace had the very same symptoms as yours...It wound up needing a new motherboard..
Once replaced it worked like a champ...

Steve...That small rod you're referring to is a thermocouple and yes, every so often you need to clean them as you described...

 

[steveblonde]

Thank you bob sorry im no plumber lol not my forte but i have to clean my thermocoupler occasionally
Cheers

 

[jyro]

Most modern RV furnaces and water heaters use a flame rod, it is not a thermocouple. This video explains it's operation.
https://www.youtube.com/watch?v=uJU3806j2CE
They can get a film on them that prevents correct operation a wire brush or emery cloth removes the film.

 

[RoyM]

We had a similar problem with ours, it was difficult to light and would not cycle back on. The problem was the pilot supply line.

 

[millartist]

Check the sail switch on the squirrel cage we replaced ours it was doing the same thing.

 

[Gary RV_Wizard]

It's not the sail switch. There would not be an attempt to light (the ignition "clicking") if the sail switch had not engaged properly.

 

[Curtisimo81]

Today when I get home I'm going to pull it apart and check it out. I'm thinking there may be a clog in the gas line even though I blew through it with air. If anyone has any other ideas please feel free to share.  I'll keep you all posted on what I find out.

 

[John From Detroit]

Two thoughts: Sometimes Propane dealers cheat. Butane is less expensive than propane and delivers almost exactly the same amount of heat (Bit more but not enough to notice) so often specifically in the south.  Dealers will pump in butane instead of propane.. And pocket the additional profit.

Propane vaporises down to almost -40 your choice of scales.. Butane only to around freezing (32F 0C)

Then we run the boiler plate.. Which follows:
When the T-Stat calls for heat the control board starts the blower (1)
The blower blows closing the sail switch (2)
The control board then opens the gas valve (3) and begins sparking (4.1)
Gas Flows (5) And ignitets (4.2)
The flame heats the flame sensor (5)
The flame sensor sends .480 volts to the control board (6)
which then detects the .480 and continues operation (*)
When the T-stat says "Enough already" (RV is now warm)
The control board shuts off the gas flow (*)
and then turns off the blower after a cool down (*)

*: At nearly every step the control board is involved. IF IT IS BAD, things will not work.. I recommend replacement boards from Dinosaur boards.. When Mine went out the Dino board was less than half the price and when  opened the box the quality of construction and workmanship, and then design was very clear to my trained eyes.

1: No 12 volt to furnace, blower motor shot
2: Low 12 volt, air ducts clogged, blower "obstructed" bad sail switch
3: Bad solenoid, Clogged Gas Jet
4: .1: Bad ignition circuit (high voltage) on control board. .2: Points too wide  (Very common it seems)
5: These do not often fail but they can
5: Bad connection, NOTE:
5 and * Bad wire.

* applies to all steps by the way So does bad wire/connection.

This should cover MOST furnace issues.

What mine did: Lit, went out, 3 times, then locked out
Testing showed good voltage from Thermocouple (Flame sensor)
Ignition was 100% (After I reset the spark gap to specification)
Problem was the chip on the control board that senses the just under 1/2 volt from the flame sensor was shot.
Dinosaur Boards supplied a repalcement, half the price of the OEM, and much higher quality from the drawing board straight through the final assembly.. Very pleased with it am I.  As of 2 nights ago it still worked (Put in in in 2012)

 

[Curtisimo81]

Ok sorry it took so long to reply it has been a busy couple of weeks.  I'm pretty sure I have found the problem.  I pulled the furnace apart and discovered (what I'm guessing is called the burner) has a big hole in it.  It appears to have rusted and the screen is really brittle.  I'm going to attach a picture to this post.  Now I just need to find where I can buy one.  Thank you for all your help with this matter.  Also if anyone knows the technical name please let me know.  Im having problems finding it. 

 

[driftless shifter]

Is it colder than it was when it worked? Mine has been doing that. It is most likely a mercaptan stink oil slug in a propane line. The furnace uses more propane than any other appliance. you smell it and hear it but it can't sustain.
i took the cover off the furnace and aimed a 300 watt halogen work light at the furnace for about 20 minutes and it started working again. I have a mobile repair guy coming this Saturday to clean it up properly.

Bill

Repair guy came by, checked my pressure at the stove top. Showed 10-11 PSI dropped to 9PSI when furnace turned on. He adjusted my regulator to 13 PSI with no demand, dropped to 11-12PSI with furnace lit. Turns out he has been doing RV's all his life and even managed a manufacturing plant in Illinois for years. He was raised Amish I have used him twice now and will continue when stuff is over my head.
AAA RV Pro McKinney, TX also listed in Anna, TX.

Bill

 

[Alfa38User]

Ok sorry it took so long to reply it has been a busy couple of weeks.  I'm pretty sure I have found the problem.  I pulled the furnace apart and discovered (what I'm guessing is called the burner) has a big hole in it.  It appears to have rusted and the screen is really brittle.  I'm going to attach a picture to this post.  Now I just need to find where I can buy one.  Thank you for all your help with this matter.  Also if anyone knows the technical name please let me know.  Im having problems finding it.

Have you tried looking here: Parts manual for 8525

 

[Curtisimo81]

Have you tried looking here: Parts manual for 8525

Yes I found an exploded its called the burner.  I actually just ordered one on amazon for like $22.00.  All the other parts stores wanted about $50.  I will say this amazon prime account has saved me quite a bit of money.  Hopefully this fixes my problem.