Hello I have a Gibson RC120C gas furnace (forced air) that has been converted to propane.

This morning I woke up the set temperature was 68 degrees and the thermometer indicated 62 degrees with a call for heat at the thermostat.
I checked the status code the red indicator was blinking 4 times, the yellow indicator was off. I turned off the electricity and turned the furnace back on and it went thru it's cycle. The red status light was lite but not flashing shortly thereafter the yellow light came on (indicating flame present) and the furnace heated the house.

I checked the ohm reading of the igniton igniter, it was 85 ohms, from what I've learned this is acceptable.

At this point this is an interminent problem (I know how difficult they can be to diagnosis). About a week ago the same thing happened when I got up the temperature was at 62 when the thermostat called for 68, that time I heard the inducer motor running, before I could go and check for codes the furnace began working properly and heated the house, until this morning.

Furnace is somewhere between 12 and 15 years old. Seback thermostat is 20 years old.

What would be the next thing to check ?
Thank You
JOB

 

When it was flashing did you hear anything running ?

 

Thanks for the quick response.

Red light was flashing nothing else, relay, inducer, etc on

 

You could try gently cleaning the flame sensor with steel wool (although you should get yellow flash if there is low signal from it). And look for cracks on the hot surface igniter. Also worth checking that the burners are clean and not plugged with rust. If you're not getting good gas flow in the igniter flame sensor area, that could cause a no ignition error.

If it was an inducer, pressure switch, or limit/rollout problem you should get a different flash code.

Finally, since it is intermittent, unplug and replug the harness connections to the board, and look for corrosion problems on the wiring terminals.

 

Was it recently converted to propane ?

 

That looks like a partial model number or a series number.

The four flashes is failure of ignition. It could be the flame sensor dirty. The furnace tries to light four times before you get the four flashes. The board then locks out for one hour unless the power is removed and restored.

You really need to be watching the furnace when it fails.

This appears to cover your furnace.........
Gibson_Installations/GAS-FURNACES/ALL-(F,K)G6RC-RL-MODELS.pdf

 

To all thanks for the input.

The furnace has been using propane since new.

How can the flame sensor be checked ? Amp draw or resistance test ?

JOB

 

Run the furnace..... with the burner firing the yellow flame sense indicator should be pretty much locked on or flicker briefly. If it just occasionally flashes on then the flame sensor rod needs to be cleaned.

The rod should be cleaned every year as part of routine maintenance.
When the burner fires.... you need to verify that the flame rod is engulfed in the flame immediately. If the burner is slow to light... that would be a problem.

 

To Pjmax thanks for the input,

I suspect the flame sensor, before I clean it (or replace it) I'm going to see if the problem becomes more apparent.

Note: The flame sensor has never been cleaned or replaced since the air handler was installed.

JOB

 

Hello my interiment problem has happened again this time I got to observe it.

Since my last post I replaced the flame sensor (as it was relatively inexpensive compared to a service call). The problem persisted after the new flame sensor installed.

Here what I observed, the thermostat called for heat and the furace began it's purge cycle, the flame ignitor began to glow orange hot, I heard a click and gas flowed, the gas hit the igniter and there was a brief blue flame (apx 1-2 seconds) before the gas shut off. Red light on, no codes, the Yellow light never came on. The furnace never shut down, the purge cycle began again, the flame ignitor again began glowing orange and the I heard a click then gas hit the ignitor and the blue flame stayed on. At this point the yellow light was on. The furnace remained on and reached the thermostat set tempature and shut off.

The furnace has been running fine for the past day, I expect the problem to return.

Any help would be appreciated, thank you
JOB