False flame sensor? bad ignitor?

I have more than one Nordyne Intertherm furnace, and after a month-long shutdown one will not ignite.

The PC bd shows a continuously flashing red fault light and this corresponds to "gas control relay shorted or false flame sensor"

I thought the flame rod verified a flame-on condition and did not interfere with initial start-up. So what and where is the the false flame sensor? Is it optical, and how do I test it? (I have a twin to this furnace only 20' away, so I switched the flame rod and that didn't help).

I tested the control valve by jumpering it and it opens fine and gas comes out and (if lit by hand) the furnace will function.

Thinking it must be the gas control relay, I changed the PC board and the exact same thing happened with the new board! Ouch!

Reading elsewhere on DIY I learned that after the burner fan starts (mine runs continuously) then the ignitor should activate, and once this happens the gas valve will open. This seems logical except that it contradicts the flashing LED and the mfrs. troubleshooting guide. You would think something as obvious as a bad ignitor would have been mentioned if that could cause this problem. Help!

 

if so what was it, I have the same furnace that you do and the same symptoms

 

I have a forced air furnace doing the same thing.

It was also throwing a "pressure valve stuck closed" error as well.

The pressure valve seems to be functioning properly though.

Did you find a solution to this problem?

 

Your best bet is to call NORDYNE Technical Support first, 1 800-422-4328, press option #2.
The Flash codes have pauses in them and are hard to read. Flash pause, flash pause is fault code 1 for one flash. It must flash with no pauses for two or higher fault codes. FLASH FLASH FLASH FLASH FLASH pause would be fault code #5 False Flame/gas valve relay shorted.
I just called Nordyne today after three days without heat due to Blizzard over Christmas weekend. Turns out that massive snow drift on my exterior AC unit is causing a short circut or power drop, enough to cause my heater not to work. after removing all control wiring and running a bypass/ jumper on the control block between R and W (jumpper wirre from R to W, turned power back on closed access door switch and low after about 30 to 45 seconds, HEAT BABY! Tech Guy named Tom S was a big help!!! Now I am just going to isolate out the AC control wires and the Blue or yellow interior control wire for the ac unit out of the unit until after that snow drift goes away, maybe next spring! Till then I can run a bypass if need be. Important note after the heat runs for a while you'll want to disconnect the bypass and allow system to cycle through its shut down process. Thanks Tom S your a life savor!!!

 

How do you know? How did you test it? Did you ever find it open when it told you the fault was that it was stuck closed?
How many wires are there on it to test? - and did you test the right ones? IF you have a 3-wire pressure switch, when furnace is off, the terminals marked NC - C should should be closed, tested between the two - and the ones marked NO - C should be open, when tested between the two with a voltmeter set to OHMS setting - when the furnace is off.