Furnace won't run after propane bottles filled. 2019 Reflection 29RL

[Tom Thumb]

Hello, new to forum and new to Grand Design. I just purchased this 5th wheel and hauled it home to Minnesota from Florida. Furnace ran fine on my three day trip home and ran fine during the two day cleaning and packing in the driveway. Last thing I did before we took our first trip was to top off the propane bottles and run the air out of the lines by running stove. First night out on our trip the furnace would not run. Turn thermostat to heat, set temp above inside temp and heard the blower start. After about 30 seconds or so blower shut down and did not try to run again, so no three try's like I have read about on other posts. Tried many times over the next few days. Turn thermostat to off, turn back on to the heat setting and listen to blower make one attempt before shutting down again. Once we got to warmer area I did a little trouble shooting. Removed outside panel and checked for anything in exhaust and intake, Clean. I had my wife try to run the furnace with me outside, I hear the blow but do not hear any click from gas valve or igniter. Removed blower cover to access sail switch (inside cover on my SFV-35Q model. Sail switch is clean as can be and checks out with my DVM. Even tried to run furnace with blow cover off and manually closing the sail switch once blower up to speed. Still no clicks heard. Thinking it might be the overtemp switch but I don't know where it is located and cannot get to the furnace inside. I can see the side and rear of furnace when I remove the drawers in my hutch but I cannot reach in that far. Is there access to the furnace from the garage if I remove the wall behind the water panel? does anyone have any ideas? Looks like I would need to remove the unit to get at the control board. Can I do that without removing all of the ducts in the rear? Does it slide out of the metal box or is it all one piece?

[Jkwilson]

Have you disconnected 12V power from the furnace? That is the reset in case your furnace failed to ignite somewhere in the process.

[TedS]

Verify that the igniter gap is correct.

[Scott'n'Wendy]

Blower shutdown with no ignition "clicking" would suggest sail switch. I would verify sail switch wiring all the way back to the mother board. Also verify ignitor connections, gap.
I would probably reconnect the propane again too.... just because.

[howson]

Tom Thumb

Good job with the initial troubleshooting.

What I'd do is remove power from the trailer (all power as a precaution) and then, as shown in the Ohms Check diagram below, verify the integrity of the thermostat signal through the limit switch, sail switch and valve switch. Initially the reading should show infinite resistance (an open). Manually activate the sail switch and the DMM should show 0 ohms, or no resistance.

If that check is good the thermostat signal is likely getting to the main board. Since the blower is coming on, that means +12vDC is also likely getting to and passing through the main board.

IF you're comfortable checking for power and If the checks above are good...what I'd look for next is to ensure the -12vDC return wire connection to the main board is good. Do that by reapplying power to the RV. As shown in the 12vDC Check diagram below, put the negative lead of the multimeter on the Y pin of the main board while putting the red lead of your multimeter on the R (power) lead with the meter setup to measure DC voltage. (Make sure and put the black lead on the Y point on the board. If you use another "ground" point there may be a false reading.) Adjust the thermostat to call for heat. Does the DMM register 12vDC? If not, remove all power again and investigate the Y pin input to the board.

The reason I'd verify the 12vDC return (aka "ground") on the board is the motor, which is running, has a different -12vDC return connection. So the +12vDC is assumed good. Clear as mud?

If everything above checks good, you may have a bad main board. :(

For emphasis, and since you're new here, let me repeat that checking "live" power can be dangerous for those not 100% sure they know what they are doing. If in doubt, hire a professional, take the trailer back to your dealer, or grab a knowledgeable friend.

Please stop back and document how it goes.

Howard

P.S. Welcome to the forum!

Ohms Check



12vDC Check (Testing Ground Connection)

[BC315RLTS]

I know you said the stove worked but have you tried turning both propane bottles off and then slowly back on. Maybe the regulator is stuck?

[howson]

I know you said the stove worked but have you tried turning both propane bottles off and then slowly back on. Maybe the regulator is stuck?

There is indeed a safety valve in the pigtail that can be triggered by an aggressive opening of the cylinder knob.

However, if it was propane related I'd expect for the OP to report that they hear the valve clicking on and that the valve cycled 3 times (valve clicking each time) with pauses between each try before the furnace shuts down. Thus why the main boards are called "three time try" boards. However, if the board does not sense the sail switch (or better yet the sail switch signal path is not completed) the furnace won't even attempt the first light. The board, in this case, thinks the fan isn't running thus it will not command the valve to open or the igniter to spark.