Problem with furnace...

goufgators wrote:
I haven't used the furnace in a couple of years. Turned it on this morning and only the fan worked. The propane burner failed to ignite. I tried it several different times with no luck. I checked the cook stove and all burners worked fine. Any thoughts re: how to get the furnace burner to work? Thanks, Larry.

Thanks to all for suggestions. Because it's gas operated (propane), and I'm not real comfortable following through on some of the suggested 'fixes', believe I'll take it to CW and let a qualified mechanic find and repair the problem. Yes, I know "CW" and "qualified mechanic" is considered by some to be an oxymoron (sp?) :) but I've had reasonably good service over the years from the one near Tallahassee. Again, thanks! / Larry

That sail switch is a switch in the air path with a plastic paddle or sail on it, wind blowing on the paddle causes the switch to operate.

Low batteries can also cause the blower to not blow hard enough.

here is the sequence with notes:

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.

Service manual.....covers your model. Pg 27/28 troubleshooting LINK

D.E.Bishop wrote:
Larry, the suggestion about the sail switch is a good one as is the one about needing to bleed the line. My suggestion is to first search for a manual for XXX Brand, XXX Model (you didn't include that info) read the manual and learn the names of the different parts of the heater and then come back with a request for help.

The first thing I would suggest is make sure you have gas at the heater control board, then check the burner tube for cleanness, then check the operation of the sail switch. If there is proper air flow down the tube and the gas valve opens when the sail switch is closed, the problem most likely is the control board. This is pretty much generic info for most heater but the manual will show you where to look for gas, and electrical test points.

Give us a shout back and let us know what is working and what isn't and maybe we can go deeper into the problem.

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Should have provided this with initial post: Suburban Mod. SH 35.

Haven't had an opportunity to follow through on your other suggestions but will soon and will report back. / Larry

What brand/model of furnace? Does it even spark?

This is generic description of RV furnace operation and applies to most DSI type furnaces.
1. The Thermostat calls for heat, sending DC current to the furnace.
2. A Time Delay Relay (can be stand alone device OR part of circuit board) is energized and passes battery DC power to the blower motor.
3. The blower motor and fans spin, pulling air from the Air Return and generating a stream of air through the Heat Exchanger and out the Ducts. At the same time another fan pulls air from the Combustion Air Intake into the Combustion Chamber and out the Exhaust.
4. The fan air stream causes the Sail switch to close as the blower gets near full speed.
5. Power flows to the High Limit Switch and onward to the Control Circuit Board.
6. The Control Circuit Board opens the gas valve and generates a spark at the DSI Igniter.
7. The Burner ignites, building heat in the Combustion Chamber.
8. Heat passes through the Heat Exchanger, warming the air circulating through the Ducts.
9. The Thermostat reaches the Set Temperature and opens.
10. Power is removed from the Control Board and the Burner shuts down.
11. The fan continues to run to cool the furnace, until the Time Delay Relay opens again.

Larry, the suggestion about the sail switch is a good one as is the one about needing to bleed the line. My suggestion is to first search for a manual for XXX Brand, XXX Model (you didn't include that info) read the manual and learn the names of the different parts of the heater and then come back with a request for help.

The first thing I would suggest is make sure you have gas at the heater control board, then check the burner tube for cleanness, then check the operation of the sail switch. If there is proper air flow down the tube and the gas valve opens when the sail switch is closed, the problem most likely is the control board. This is pretty much generic info for most heater but the manual will show you where to look for gas, and electrical test points.

Give us a shout back and let us know what is working and what isn't and maybe we can go deeper into the problem.

Victory402 wrote:


You may just have air in the line, mine takes a lot of tries before it lights every fall for the first time. Keep trying...

X 2 RUN THE BURNERS ON THE COOK TOP FOR A COUPLE OF MINUTES, THEN TRY IT AGAIN.

Thanks...but what's a "Sail Switch"?

It's a safety switch that wont allow the furnace to light without proper air flow from the fan.

You may just have air in the line, mine takes a lot of tries before it lights every fall for the first time. Keep trying...

donn0128 wrote:
Sail switch appears to be a common theme.

Thanks...but what's a "Sail Switch"?

Sail switch appears to be a common theme.