Atwood Furnace Issue

[Frank C]

Furnace had been functioning normally for the last 4 years with no issues until this latest trip on a cold morning.  Upon turning the thermostat to FURNACE setting, the furnace blower would start and I could hear the burner ignite.  Hot exhaust gas from the burner was exiting the exterior exhaust port as usual, but after a few seconds the burner would shut off, blower still running, then the burner would ignite again a few seconds later, then shut off again, then a 3rd time for the burner igniting and shutting off, then the entire furnace including the blower would shut down.

No errors on the thermostat display but the red LED on the circuit board inside the Atwood exterior furnace access panel shows a pattern of 3 blinks, then a 3 second pause, then 3 blinks, etc.  The troubleshooting info found on the label inside the cover says that error code means “ignition lockout fault”.

Here’s what I’ve checked so far:

-I made sure the thermostat set point is high enough (I tried 72, 75 and 80 degrees) so that the furnace should be running continuously since the ambient temperature inside the camper was around 60 degrees. 

-Propane tank is full, and propane is flowing to all other gas appliances (stove and Truma).

-I let the stove on for a bit to purge any air out of the propane line. 

-Removed and inspected the sail switch, no fuzz, spiderwebs or lint buildup.  Sail moves freely and I can hear the switch activate.

-Hit the OFF/RESET switch on the furnace and waited 1 hour (troubleshooting manual mentions both a soft timed lockout and a hard lockout that requires reset.

-DC power is good, battery voltage at 13.2 volts (connected to shore power so batteries are charging).  

Any thoughts on what else to check before I give Atwood and/or Oliver a call? 

[Tom and Doreen]

First off I don't have one of these furnaces so this comment probably isn't worth the time you're taking to read it but it sounds to me like your furnace is not 'seeing' a flame  which would indicate a faulty flame sensor; most furnaces have a mechanism like this.  

[topgun2]

53 minutes ago, Tom and Doreen said:

it sounds to me like your furnace is not 'seeing' a flame  which would indicate a faulty flame sensor; most furnaces have a mechanism like this.  

Yep -  

since you've checked the air flow and it is OK then about all that is left is either you are not getting a "spark" for ignition (you know that this is also good because the furnace does ignite) or the furnace does not sense that you have a burner flame once it is ignited. 

If it were me - I'd try to clean the thermocouple - it will look something like THIS one.

Even if you are successful in cleaning it and get the furnace to function, I'd strongly consider replacing it.

Good luck!

Bill

p.s.  NOTE!  It is highly likely that the thermocouple on your furnace is different from the one referenced above - I only wanted you to know what it looked like, not that this one is a replacement for yours.

Edited June 29, 2023 by topgun2
added detail

[Shawna and Scott]

My gas furnace at home was doing this every couple seasons and it has always been the flame sensor. I just started cleaning it before I start to use it each year at home and so far no problems. 

I am not familiar with your furnace but it should have a flame sensor and it sounds like the exact same problems I was having. If you can find the flame sensor it is easy to clean.

Sorry couldnt be more help.