Furnace problem

[Stormclouds]

Furnace problem! The furnace just blows cold air for about 15 seconds and shuts off. Put in new thermostat to no avail...steps taken so far.

Removing fuse
Made sure batteries are fully charged

Any suggestions? It's cold!

[paverdave]

Hey Stormclouds...Welcome to the Forum. Tell us a little more info on the trailer.....make and model and make of furance..so we can help you get some heat in the trailer...

[5picker]

Do you have propane?

Have you lit all three stove burners at the same time and verified strong flame at each of them?

[oxcamper]

One thing is to check to make sure your thermostat is on AUTO.

[flhtci2006]

Maybe the sail switch? Cheap and easy to replace. Something easy and narrows the problem, access the wiring to the furnace circuit board and look for the 2 thermostat wires. Disconnect/cut where they are tied together. take the 2 thermostat wires that go to the furnace curcuit board and tie them together (this takes the thermostat and its wires out of the picture. If the furnace comes on and works properly, the problem is in the thermostat or its wiring or, it you have one, the thermostat control unit. If the furnace does not work, could be one or more of 3 things: 1. sail switch, 2. high limit (overtemp) switch or 3. the circuit board. More info, the sail switch tells the circuit board that the fan (not the blower motor) is operating and that propane and ignition can start (this fan circulates the air thru the burner and exhausts it outside). If the switch fails, the unit will never start the propane and ignition sequence. The high limit switch isa thermistor that should the burner area get too hot, it shuts the system down. If it fails, the furnace will think its be overtemped and won't do the propane ignition sequence. So, one side says you have airflow for the ignition/burn process and the other end determines if the unit is overtemping and shuts it off. All that goes through the circuit board.

I too am in the learning process. If someone thinks I am wrong, I welcome "kind" corrections. Don't need assholic remarks.

Storm"y", keep us updated please.

Signed,
Coronavirus free but old and senile.

I am going thru something similar. My thermostat with turn the AC on but not the furnace. The furnace, in my case, does nothing at all. I short the thermostat wires together and it came on and worked as advertised. My assumption is for me, it's the wiring to the thermostat, the thermostat or the thermostat control box. Just giving you some info for your mental database.

[nayther]

is there a circuit board with an LED? if so the LED should flash a code that will tell you why it's not coming on. You clear the code by cycling power. the circuit board are also known to crap out.

[Stormclouds]

2010 FR Flagstaff 26rls

[Stormclouds]

Yes strong flame in all 3

[Stormclouds]

I have no access to circuit board

[Stormclouds]

Originally Posted by paverdave

Hey Stormclouds...Welcome to the Forum. Tell us a little more info on the trailer.....make and model and make of furance..so we can help you get some heat in the trailer...

2010 FR Flagstaff 26RLS

[Stormclouds]

Originally Posted by oxcamper

One thing is to check to make sure your thermostat is on AUTO.

Yes it is...thanks

[Stormclouds]

Originally Posted by 5picker

Do you have propane?

Have you lit all three stove burners at the same time and verified strong flame at each of them?

Yes...all 3 have strong flames

[Stormclouds]

Originally Posted by nayther

is there a circuit board with an LED? if so the LED should flash a code that will tell you why it's not coming on. You clear the code by cycling power. the circuit board are also known to crap out.

No circuit board

[Stormclouds]

Originally Posted by flhtci2006

Maybe the sail switch? Cheap and easy to replace. Something easy and narrows the problem, access the wiring to the furnace circuit board and look for the 2 thermostat wires. Disconnect/cut where they are tied together. take the 2 thermostat wires that go to the furnace curcuit board and tie them together (this takes the thermostat and its wires out of the picture. If the furnace comes on and works properly, the problem is in the thermostat or its wiring or, it you have one, the thermostat control unit. If the furnace does not work, could be one or more of 3 things: 1. sail switch, 2. high limit (overtemp) switch or 3. the circuit board. More info, the sail switch tells the circuit board that the fan (not the blower motor) is operating and that propane and ignition can start (this fan circulates the air thru the burner and exhausts it outside). If the switch fails, the unit will never start the propane and ignition sequence. The high limit switch isa thermistor that should the burner area get too hot, it shuts the system down. If it fails, the furnace will think its be overtemped and won't do the propane ignition sequence. So, one side says you have airflow for the ignition/burn process and the other end determines if the unit is overtemping and shuts it off. All that goes through the circuit board.

I too am in the learning process. If someone thinks I am wrong, I welcome "kind" corrections. Don't need assholic remarks.

Storm"y", keep us updated please.

Signed,
Coronavirus free but old and senile.

I am going thru something similar. My thermostat with turn the AC on but not the furnace. The furnace, in my case, does nothing at all. I short the thermostat wires together and it came on and worked as advertised. My assumption is for me, it's the wiring to the thermostat, the thermostat or the thermostat control box. Just giving you some info for your mental database.

I have no access to circuit board

[NorCal Rich]

Originally Posted by Stormclouds

No circuit board

You'll want to locate the circuit board and flashing lights, just repaired a similar situation on my rig, (los battery and sail with)
The flashing lights will help narrow down the possibilities
Number of Flashes:
1 w/ 3 second pause Air/flow limit fault
2 w/ 3 second pause Flame Sense Fault
3 w/ 3 second pause Ignition Lockout Fault
Steady ON no flash Internal Control Failure

Attaching a couple of articles that helped a little

Also good stuff from Darren at My RV Works
http://myrvworks.com

https://www.youtube.com/watch?v=0t8vRuGdZLw

Best of luck to you man

[boondocking]

If the blower is starting up the thermostat is OK.

If the batteries are not above 10.5 volts the blower will not run fast enough to activate the sail switch. Check the battery voltage.

If voltage is above 12 volts then...
Listen for a clicking sound while the blower is operating. If the furnace fan inside the trailer is too loud go outside and listen at the exhaust for a clicking sound (igniter operating).

If there is clicking sound then the sail switch is OK, but the gas valve is not opening, could be a defective gas valve or circuit board. No clicking sound the circuit board or igniter is defective.

[paverdave]

Originally Posted by boondocking

If the blower is starting up the thermostat is OK.

If the batteries are not above 10.5 volts the blower will not run fast enough to activate the sail switch. Check the battery voltage.

If voltage is above 12 volts then...
Listen for a clicking sound while the blower is operating. If the furnace fan inside the trailer is too loud go outside and listen at the exhaust for a clicking sound (igniter operating).

If there is clicking sound then the sail switch is OK, but the gas valve is not opening, could be a defective gas valve or circuit board. No clicking sound the circuit board or igniter is defective.

^^
X2

[Bill Broderick]

Furnace fires up good but when temp is reached and gas shuts off blower fan keeps running. The only way I have found to shut it off is to pull the fuse or hit the reset switch.

[5picker]

How long does it run after the burner shuts off?

The fan won't shut off when the burner shuts off because it has to cool the firebox before it can shut off. Mine runs for maybe a minute (or a bit longer) after the flame stops. It will sometimes come back on for 20-30 seconds to re-cool if necessary.

[Kuba]

Sail switch/pressure switch. Also check your fresh air intake and exhaust outside for obstructions