Suburban Furnace stopped working

[Boozecamp]

Furnace has been working fine up thru last night. This morning I get up and it's 35 outside, 43 inside, no wind, and furnace will not kick on. Checked the easy stuff first, Propane tank is half full, no breakers tripped. When I get home from work this evening, I'll check fuses, change over to the second propane tank which is full. Anything else I can do myself before calling the $$$ tech guy out for a house call? I did try cycling the system off, waited a few minutes, then turned it back on, no go! Is there a pilot light, or is it electronic ignition?

[midnightsadie]

from yout last post, I think your battery was low and the electronics seen it and shut you down, battery back up and it worked.

[enblethen]

Just because the thermostat is getting power does not mean the contacts or solid state device is closing sending message to the furnace.

[Boozecamp]

Good news, I hope its not temporary.
The wife turned the thermostat to "off" for a couple hours, and turned it back on and it fired right up and is working now. go figure....
The Thermostat has a digital readout, plus the little green LED that toggles from Fan/AC/Furnace/Off was eluminated, so that's how I knew it was getting power. She also checked the battery indicator and it's fully charged.
Overnight the furnace was on, set to 58 deg. I turned it up to 70 when I got up and nothing happened, no blower, no clicks, nothing. Normally it would immediately click, then start the blower within 3 seconds, followed by ignition of burners and then heat. Just the way they are supposed to work. BTW: this is a fairly new unit, 2014. only used the furnace this winter season.
A post earlier suggested a relay or cutoff switch that is sensitive to back-pressure. Is it possible we could have accidently covered a register with a rug (covering 1 of 5 registers) to cause enough back-pressure to trip a relay? Just scratching my head to determine cause.
Thanks for everyones thoughts/suggestions.....

[wa8yxm]

One thing if you were boondocking: Battery state of charge. here is a document you may find helpful.

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.

[enblethen]

How did you determine thermostat is good?
What is model of the furnace?
What is make and model of the thermostat? Does it work just furnace or does it control the AC unit?

[n7bsn]

Boozecamp wrote:
The thermostat works. Blower doesn't work, I'll check for clicking at unit outside. And check battery.

When that happened on ours it was the controller board. Replaced it with a (compatible) Dinosaur (brand) board and everything worked

[midnightsadie]

bad battery will cause this,

[phillyg]

It took two techs five hours to correctly diagnose and repair the brand new Suburban unit in our new FW last week. I don't believe they were running up labor hours because the service manager waived all but one-half hour of diagnostic time.

We weren't hearing any ignition clicking. Turned out to be a bad sail switch and limit switch. The blower was coming on and cut off almost immediately when the sail switch failed to open. When they replaced the sail switch and bench-tested the unit it worked fine, until they reinstalled the unit in the FW and the outer case apparently caused enough back-pressure to make it fail again. Unless you have some level of expertise fixing these things you might end up chasing solutions all day and never get it fixed. I suggest you find a competent RV tech with Suburban experience.

[Boozecamp]

The thermostat works. Blower doesn't work, I'll check for clicking at unit outside. And check battery.

[enblethen]

Is the blower running at all?
If no you have lost power or the thermostat has gone bad.
Remove cover from thermostat and connect the two wires from the furnace together. Blower should start immediately and produce heat in 15-20 seconds. Separating wires should turn off heat and put the fan in cool down mode and then shut off.
If blower runs, your voltage maybe too low to produce enough air movement to operate sail switch.
Sail switch could be dirty. Locate it or even blow the furnace out with a can of compressed air.

[RoyB]

If you are camping off the power grid it could be your battery is low... As stated above you have to hear the blower work first before it will fire the propane...

If you have only one battery the golden rule is one battery one night when camping off the power grid and having to run the furnace...

Another quick check is to use the stove top for a few minutes to ensure the propane is working...

Roy Ken

[Road_Runners]

Does the air blower run, but the propane doesn't ignite? If so, it could be your out of propane or it could be the sail switch went bad. If it is the sail switch the unit will have to removed to replace it. The sail switch tells the operating mechanism that yes there is air flow the propane can be ignited. If the sail switch is inoperable the propane will never be ignited.

[dalenoel]

If you have never had to light the pilot before then it is electronic ignition. Can you hear the clicking of the electronic ignition? If not then it is not getting a signal from the thermostat or not acting on that signal. If it is clicking then it is a problem in the ignition. If you can see the spark then it is a fuel problem. May be no fuel or may be a valve not opening and getting a signal.

Is the fan coming on prior to the ignition sequence? If not then the purge sequence is not happening and that will stop ignition.

Think through the steps that need to happen, what you have heard in the past, and see where the steps stop and start looking from that point on.