Can anyone please help me with the problem I have on Rudd gas furnace model# UGDG-07NAMCR from 1990. Problem I'm having is after I set the thermostat in heat mode and set it at 73 wihile room temperature is 68, the inducer fan comes on for about 30 sec., then the glow-plug starts glowing for about 10sec., then the fire roars on all 3 burners, then the main blower run.

However, after 20-30 second while the main blower still running, The fire went out out. In another 10 sec. the glow plug starting to glow again , then the unit ignites again, then it repeats what it did at first for many times.
Eventually, after several attempts re-lite it itself, the furnace stopped working. So, I unplug and plug the ac-power to reset it, and it worked like at the first attempt.
From what I’ve been reading, the flame sensor might be the issue. However, I couldn’t find the flame sensor on it.
On the right side, there is a glow-plug.
On the left side, there is a round-flat sensor with 2 wires, look like a button.
But there is no long skinny piece flame sensor with single wire.

Please let me know, where can I find the flame sensor on this unit. Or is the glow-plug also serve as a flame sensor?
And also, how do I attach a picture here?

Thank you.
Mike

 

Hi Mike & welcome to the forums. Some furnaces used the ignitor as a flame sensor. Clear, well lit pictures are always a help. The best way to do pictures is to post them on a photo sharing site such as photobucket & provide a link to the album here.

 

So, I the problem on my RUUD furnace most likely due to faulty/dirty Glow plug? Or not enough airflow? or The Board?
Can I clean the igniter(Glow Plug)? Or does it need to be replaced? Thanks

 

Pictures first please, Mike. Need shots of the burner area particularly the ignitor also of the control board (close enough we can see & read the terminals.

 

Attached is the pic. Thank you

 

It would appear your furnace uses the ignitor as the flame sensor. I will try to find a manual or wiring diagram but Rheem manuals are often difficult to locate. Is there a wiring diagram on the inside of the blower door? If so can you get a good picture of it?

 

Attached is the wiring diagram and the gas valve. Thx

 

Thanks mek. I can't read the diagram but it looks more like a troubleshooting guide than a wiring diagram.

At this point, I think I'd try a new ignitor.

 

Yesterday morning and this morning, the heater did not work. Room temp=68, thermostat set to HEAT at 72.

So, I did turn the switch at the thermostat from HEAT to OFF, then to HEAT again yesterday morning and this morning., and the furnace was working once I did that.

I guess, the problem is the electrical. The thermostat was replaced in 2006.

Please let me know, if the problem is either the circuit board or the digital thermostat.

Thanks
Mike

 

When you do what you did, you are resetting the contol board. The problem will come back.

 

Yes, you're right. problem keep coming every morning I have to do that.

So, is that mean the furnace is locked out because the furnace keep trying to ignite due to the fail flame sensor?
OR
Is the circuit board defective?
OR
Is the thermostat defective?

Thank you

Mike

 

I'm guessing but my best guess is ignitor. It's easy enough to eliminate the thermostat by removing it & connecting the wires from terminals R & W together. This takes the thermostat completely out of the picture. If it does the same thing as in your first post, I'd say the stat is not the problem.