Please post which furnace you have, assume it an Attwood. Found the following when searching for three flashes, hope it helps.
Fault LED Indication
Internal Circuit Board fault Steady on, no flashing
Limit switch/Airflow problems 1 flash with 3-second pause
Flame Sense fault 2 flashes with 3-second pause
Ignition Lockout Fault 3 flashes with 3-second pause
So it appears you have an ignition lockout fault.
That would mean that the electronics is not detecting a flame that MAY be there.
Maybe a bad ground at the electronic board.
Or, the sparking you hear may not be taking place at the place it should be.
Possibly a bad spark electrode or high tension wire.
A "flame sense fault" would mean that the board sensed the flame at trial for
ignition, but then lost the flame signal.
This electronic board senses the flame thru flame rectification.
Basically, a flame will pass a DC electrical current. In this case thru the spark electrode to ground (the burner).
So your "spark wire / electrode" is also part of your flame sensing circuit.
To reset your board all you need to do is:
1. Turn your t-stat on off switch off.
2. Turn down the temperature so the bimetal points will open.
And wait for the fan to shut off, if it hasn't already.
To restart, flip the switch back on and turn up the t-stat.
You can go to the Atwood site at : http://www.atwoodmobile.com/heating-...ii-series.aspx
There is some information here and a trouble shooting guide.
BUT remember you are working with LP gas, be very careful. If you are the least bit unsure of what you are doing,
please take it to a dealer. It's better to pay a few bucks and be uninjured and still go camping.
Try shutting off your tank, light your stove to burn off the gas (reduce the pressure in the gas line) then turn off stove.
Then S L O W L Y reopen your tank. There was a thread describing how by opening the valve to quickly will cause the
regulator to stick. Gas will flow but not at a large enough volume for the furnace to work.