Furnace won't ignite

twins89 wrote:
It was a stuck sail switch.

That's the elusive 1 out of 10!

Thanks for the update!
Glad you had an easy fix!

It was a stuck sail switch.

9 out of 10 times the culprit is low voltage. See about plugging into a generator or other AC source for a little bit OR hook up a set of jumper cables to the tow vehicle (running of course) to charge the trailer battery. Try to start the furnace while hooked up to this exterior power source.

As the OP stated, the stove is working. Depending upon the system layout, the furnace may be the farthest appliance from the propane cylinder. Try igniting a few times if the cylinder has been changed recently. My stove is right next to the furnace and it usually takes one or two attempts to get it to light the first time out.

Did they recently change propane bottles? Did they try waiting a little longer on pilot to purge the air before hitting the igniter? I had that problem on our new to us fiver.

Low voltage can slow the fan motor sufficiently to not allow sail switch to operate.
Sail switch could have small piece of debris not allowing it to close the contacts which prevents the circuit board from getting power. You could use a can of compreesed air to blow out furnace area.

Could be low voltage in batteries. Is there anything obstructing the air input/output. My friend had a wasp nest in his intake vent. Also could be the Ignitor is dirty or bad.