furnace dose not light

Ignitor lock-out.

After 3 attempts to lite off it will go to lock-out.

Low gas pressure...should be 11" WC with at least 50% of other gas appliances in service
Blocked exhaust...creates an imbalance in air/fuel ratio
Spark electrode dirty/out of position......clean electrode with emery cloth/set spark gap to 1/8"
Spark electrode wire bad
Circuit board....bad connection/contacts on board (pull connector/clean contact surface with pencil eraser) OR the board is bad


Clean up the spark electrode and board contacts and check ground connections on furnace

I had a similar problem a couple of years ago. RV Tech came out, pulled the connector in the outside access compartment and sprayed it with electrical contact cleaner and plugged it back in. It's worked fine ever since then! Amazing what a little cleaning can do - almost as amazing what a little corrosion can do!

I don't recommend electrical contact cleaner , some contact cleaners make plastics and connectors on control boards brittle and may crack or shatter.
When was the last time the heater was used?
If it has been a long time you may need to clean burner orfice and or flame sensor
Other than that everything Old-Biscuit said in earlier post

There are many causes.. For example if the blower does not blow hard enough (low battery, Bad connection, Bad motor, Blocked air duct, Faulty sail switch) the sail switch will never close and the unit will time out.

if there is no LP flow (Empty Tank, valve off, faulty regulator, bad solenoid valve, clogged orifice) then it can not light

If the ignition system does not make sparks (Spark gap too wide, Wire or connector fault (Bad) bad control board)

And in this last case, it will iight...for about 3 seconds 3 times, If the control board fails to sense the flame (Bad thermocouple (Flame sensor) Bad wire or connection, bad control board) it will lock out.

On the model you have I believe there is a single high-tension wire that carries both the spark voltage (Roughly 1,000 wolts) and the flame sense voltage (Roughly 1/2 volt, or .480 volts or 480mV if you want to know the peoper voltage).

I should point out I have the same furnace.

In my case it was the last fault. It would light for 3 seconds.. i checked everyting. And I mean EVERYTHING several times over.. Wound up ordering a new Dinsosaur Fan-50 control board from American RF in California (not to be coufused with the company that changes my oil, American RV, Burton, MI). and the problem vanished.

IF that is what your problem is this is my theory.

The change over from SPARK generation to Flame sense went wrong and it hit the flame sensor chip with the kilovolt spark power, Frying it soundly.

I suspect Dinosaur boards thinks this is what happened too.. WHY? Well on the Dino Fan-50 is a device, a Gas Discharge Tube. Often used to protect senistive electronics from over voltage.. This is a very robust protective device,,, I can only think of one reason for it to be there. They have the same theory I do so put in a protection device.

The quality of the Dinosaur board was very impressive.

What furnace temp settings? Have an 04 Carriage with a Carrier AC/H unit and am attempting to set the furnace to run instead of the Aux heat on the AC. Set Wall thermostat to 80+/- and the hand held control to 77, furnace kicked in. When I lowered the W/T to mid-upper 70's, furnace shut off. What one controlls the furnace what temp setting would you set for 70-75 degrees?

70daytona, You'll have to interpolate. I'd set it to what is comfortable. Thermostats are always inacurate.