Hydro Flame Furnace 8535 -II

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Feb 22, 2006
La Grange, California
Fan works...no flame! Replaced sail switch! I read 12 volts at the input to the ignitor board with the fan operating...so I'm assuming the limit switch is also working. Can someone tell me how to remove the furnace so I can further troubleshoot and replace if necessary. Also...what should I read at the "hi-voltage" output wire at the ignitor box? I have a '92 Alpenlite Fifth Wheel and perhaps it's just time to replace with the Excalibur...or not! I thank all of you for any additional info you could offer. Regards, Jim
Thank you Gary,
You mentioned "circuit board." I am assuming you are relating to the ignition board...the small box that is mounted on a side wall next to the motor??? This is where I tried to read the "hi-volt" signal. Approximately, 10 - 12 seconds after the motor starts I do hear a click and the voltmeter tries to read something coming off of the "hi-volt" connector of the ignition board. Should I be trying to read current, rather than voltage? The digital meter just kind of freaks out during this spark process.
Again, thank you for any reply.
The click and the meter freaking out is the high voltage going out to the igniter at the burner oriface to light the gas. Since it freaks the meter, there must be some sort of voltage being sent down the wire, so the next step would be to trace the wire into the burner area and see if you can tell if there is a spark across a bare metal probe to some metal part of the heater at the end of the oriface when it tries to light.  The wire probe should be in a ceramic piece. On my old Winnebago, I accidently broke the ceramic piece on the ho****er heater, and I would get the high voltage, but since the ceramic was broken, it didn't produce a spark. As luck would have it (seriously), my local dealer had a junk hot water heater of the same brand and the ceramic igniter was still good. I got it for just the labor it took for them to remove it from the junker. Replaced on my hot water heater, and it lit fine.
2006-F350...Thank you!
With that in mind, I walked out into our dark barn with flashlight in hand. With the furnace cover open I peered into the fire side of the unit, focusing toward the end of the "hot wire" coming from the ignition board. All I see is something that resembles the plastic/rubber casing surrounding a sparkplug. At this point I lose it...it goes into a unit of it's own. Anyway, with all light out, I connected the thermostat relay wire and waited the 10/12 seconds for the click...total darkness, no spark...fan only.  I repeated this several times with the same negative results. RATS!

Not sure if I wanted to see a spark or not...at any rate, I didn't. I guess I need to remove the furnace and look for evidence of failure...not sure what I will be looking for. Once I remove the gas line and pull the furnace out does anyone know of a method to test the unit...outside the rig. It appears to me...in order to remove the unit I need to unscrew all the outside perimeter screws. The tech at a local RV shop says there are only a couple inside screws on the top...I fail to see an easy means to remove the unit without removing the outside casing. Any input from someone that has walked this path would be most appreciated. Thank you all for any input.
Regards from Jim and his cold wife.

Don't rush into removing the furnace quite yet. There are some others things to check first. Does your propane stove work in high flame? If not, the main gas valve may be shut, the propane line and/or regulator may be full of debris, or the propane sensor may have shut the system down for safety. Check those first. After you remove the outside panel of the furnace, you should be able to see the burner tube, the gas orifice, and the ignitor. If you don't see a spark but have 12V at the board, chances are the board is bad. You can disconnect the high voltage wire from the board and, with an insulated wire screwed to a good ground, hold it about 1/8" away from the top of the high voltage coil and see if there's any spark there. A voltmeter is almost useless 'cause it can't read a short duration, 10,000 volt pulse very well. Besides, it can fry your meter :p If you see a spark that way, chances are good that the gap between the end of the ignitor (near the end of the burner tube) is too large (re-position it according to mfg's instructions) or it may be shorted out by the presence of carbon from a dirty (yellow) flame. It should be blue. The ignitor can be removed and cleaned with a rag and some solvent. Next thing to check would be the gas valves themselves. They're actually electrically operated solenoids, and there are usually two of them (for sfaety reasons)mounted together. When you turn on the furnace, you should hear a click from them, bt it may be difficult to tell if both are operating (as they must). If not, check for 12 volts on their terminals. No 12 volts? Check wiring back to circuit board, check the inline diode with your meter set to ohms (it will read a resistance when you have the black lead on the cathode (the end with the black band) and the red lead on the anode. When you reverse the two meter leads, it should read infinity. If it reads infinity either way, the diode is bad. Also check the limit switch with the meter. It should read almost zero ohms. Check the solenoids for continuity. They will probably read somewhere between 100 and 1000 ohms if o.k..After all this, you can further check the solenoids, but be very careful!: Turn off the propane at the tank.  Remove both wires from one of the solenoids. Connect a ground wire to one of the terminals (doesn't matter which one) and with another wire connected to 12 volts thru a 5 or 10 amp fuse, briefly touch it to the other terminal several times. A definite click should be heard each time. Reconnect that solenoid and repeat the process on the other one. If either one fails to give you that click, it's bad (gummed up or corroded) and needs replacing.  You should be able to do all these things without removing the furnace, but you didn't tell us which make and model you have. That would be most helpful.

A word about ignitor boards: Those for water heaters typically send out one spark to light the flame; those for furnaces send out multiple sparks. Sometimes a furnace board will not do so, and the furnace may not light. If in doubt, most reputable RV repair shops have board testers and will check them for you. If you need a replacement and you have an Atwood or Suburban furnace, I would suggest replacing it with a Dinosaur board.http://www.dinosaurelectronics.com/
You mentioned "circuit board." I am assuming you are relating to the ignition board...the small box that is mounted on a side wall next to the motor??? This is where I tried to read the "hi-volt" signal. Approximately, 10 - 12 seconds after the motor starts I do hear a click and the voltmeter tries to read something coming off of the "hi-volt" connector of the ignition board. Should I be trying to read current, rather than voltage? The digital meter just kind of freaks out during this spark process.

Yes, that's the board I mean. Your meter is seeing a high voltage pulse of very short duration, much like you would see if you tried to use a VOM to measure volts or amps on a spark plug wire on a gas engine. You won't get a meaningful volt or amp reading with that sort of meter, but the fact that it "freaks" indicates you are getting output from the board. That suggests it is good, though does not quite guarantee it.

The few Atwood Hydro-flames I have worked on have had their major components accessible once the interior and exterior covers plates were removed. Not necessarily easily accessible, but within reach.  They also appeared to slide out through the exterior wall without major work, but I never had to do that. Never replaced an igniter either, so I'm learning from you as we go along.

You might want to check out these articles on diagnosing DSI furnace problems:



Here's a good source for Hydroflame igniters:  http://www.marksrv.com/hydroflameparts.htm
Gary and Karl and 2006 350-
WOW...What input!  First off, thank you!!! Tomorrow morning I shall grab the printouts of this thread and beam toward my rig with a larger bucket of troubleshooting knowledge. I will report back...hopefully wearing a smile of success.
Again, I am most grateful.
Jim ... and his shivering companion..

Thanks to all of you I was able to locate the problem... while learning a little more about "how things work" on a rig. The ignition board was sending a signal to the "gas valves", both of them...however, on one valve I found the yellow ground wire was not tightly attached to the connector. With the help of a real long "long nose" plier I was able to "squish" the female end of the ground terminal lead and reattach it to the valve. It did appear that there were two valves and the other one appeared to be okay...however, without it's companion in working order it, too, refused to ignite. Once I felt I had restored the furnace to normal, I went inside the rig and turned the thermostat on. With nail biting apprehension I waited to hear the click...and then the welcome sound of the propane thrusting in to the burners. YIPPEE!

On behalf of myself and my "soon to be warmer" wife, thank you!
Exactly Karl and congratulations to you gentlemen for your astute knowledge and the fine tuning of the situation.  This is why this is the most important forum for RV'ers on the web or anywhere else for that matter.

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