Furnace "lockout"?

TheWilliamsFamily wrote:
Hello all. It is starting to get cold at night in Texas and my furnace is giving me grief. When I turn the thermostat up the blower turns on, the igniter sparks up it runs for 20 to 40 seconds and shuts down. I have checked the fuse and cleaned all the connections. Blew the whole thing out with compressed air. Made sure the vents were open and uncovered and register was unblocked. I'm sure it's a more technical issue but I'm hoping to fix it myself rather then take in for service. Any help would be great.

It is a Atwood Hydro Flame 8940 111

Is furnace in a RV or home??.... If either, the brand and model is always the best place to start...

Mine does this after it sets for a long time with out use. Some times I have to go through the 3 tries to start 4 times before all the air gets out of the gas line and it works likes it should.

Man does that sound familure..

It sparked
It lit
It shut down 3 times, then it locked out.

Now I did a major diagnosis job, I verified the thermocouple (which on my unit doubles as one of the spark contacts) was putting out the required 480mV (it was) I checked many other things and finally decided the control board was bad.

I contacted American RV in California (NOTE: Many States including Michigan and Georgia have companies called American RV, all different companies, you want the Californian one) (The other two I mentioned one put my new A/C on and the other does my oil changes).

I ordered a new DINOSAUR board, less than half the price of an OEM board.

Now I'm trained as an electronics technici9an, i've dabbled in electronics for ovewr 50 years.. When I opened the box my first impression was QUALITY, and upon closer inspection and comparision to the OEM board it was QUALItY!!!!!!!!!!!. Then I turned the board over and well. lets just say the font got bigger and more exclamation points. .. I have a theory as to what killed my OEM board.. Well seems the good folks at Dinosaur boards share it because right were it needs to be to prevent the failure I had is a handy dandy Gas Discharge type Spike supressor. I did have to make a minor change to how I mount it (used a Zip-Tie or two) but other than that.. Straight plug in replacement. and as of last week when I last used it.. Still working. (it was 2012 when I installed it)

If you want I can .. oh heck I will... Here is my trouble shooting boiler plate:
(This was created as I diagnosed my Furnace back in 2012.. Lots of time went into it, it's been vetted, I think I had to add one line after that as there was one thing I missed.. but if anyone knows anything I missed, PLEASE TELL ME, thank you.. nOTE most of it also applies to water heaters and all other DSI devices)

This document was created while I was diagnosing MY furnace.. I am told I missed one possible issue... Sadly I forget if I updated the document or not and the issue Bad connections anywhere along the line can lower voltage

When the T-Stat calls for heat the control board starts the blower (1)
The blower blows closing the sail switch (2)
The control board then opens the gas valve (3) and begins sparking (4.1)
Gas Flows (5) And ignitets (4.2)
The flame heats the flame sensor (5)
The flame sensor sends .480 volts to the control board (6)
which then detects the .480 and continues operation (*)
When the T-stat says "Enough already" (RV is now warm)
The control board shuts off the gas flow (*)
and then turns off the blower after a cool down (*)

*: At nearly every step the control board is involved. IF IT IS BAD, things will not work.. I recommend replacement boards from Dinosaur boards.. When Mine went out the Dino board was less than half the price and when opened the box the quality of construction and workmanship, and then design was very clear to my trained eyes.

1: No 12 volt to furnace, blower motor shot
2: Low 12 volt, air ducts clogged, blower "obstructed" bad sail switch
3: Bad solenoid, Clogged Gas Jet
4: .1: Bad ignition circuit (high voltage) on control board. .2: Points too wide (Very common it seems)
5: These do not often fail but they can
5: Bad connection, NOTE:
5 and * Bad wire.

* applies to all steps by the way So does bad wire/connection.

Main flame is lighting BUT failing to 'prove' that is is lit.
Flame 'ionization' generates a milivolt signal that uses spark electrode to go back to circuit board to 'prove' you have flame vs raw gas flowing

As suggested...
Pull connector and clean contact surface.
Also check pins inside connector....not bent and that they can make tight contact when connector is pushed back on

Clean electrode ......soot/carbon
Make sure it is centered directly over burner slots
Check ceramic for cracks
And make sure ground is clean/tight

Hi... clean flame sensor with fine sand paper. Maybe it is dirty. That can happen over time with normal use. Jim2007.

Does the other propane appliances work properly?
Check manual to insure that the spark ignitor/ flame sensor is directly in the flame.
Clean contacts on the circuit board multi-wire connector. Use white pencil eraser if you have one. Red ones work as long as they are clean.