First, thanks for any help you can offer. I've never done any hvac work, but am reasonably handy, and have other construction and electrical experience.

Last spring, our furnace stopped working. Turning the thermostat down did nothing, no blower, no heat. Since it was warming up (May in Portland, Oregon), we left it alone. Late September has us thinking about winter, so here we are.

For starters, I have an Gibson KG6RC-100N-16B furnace, and a Honeywell RTH7500D1007 thermostat.

We had an old igniter on hand, so tried replacing it, but with no success. My approach so far would be to start back at the thermostat, move to the draft induction fan. I read a post somewhere else that said to test the thermostat by shutting down power to the furnace, connecting the wires leading from the thermostat, then turning the breaker back on. The problem I ran into right away was knowing which wires to connect. I have three, labeled G, R, & O/B.

Question 1: Is this the right way to begin, and if so, which wires would i connect?

Question 2: Along the way, I tried plugging the condensate pump into a different (unswitched) outlet, and nothing happened. Would this potentially lead to failure to start?

 

A bit of progress, but still no resolution. When I turn the thermostat on the draft induction fan kicks in, and you can see a bright orange glow from the igniter. The blower never kicks in though.

The blower *will* run if the thermostat is set to fan only. If it is set to heat, the blower will not run.

Should I look at the flame sensor next?

 

Welcome to the forums.

The igniter should heat for xx seconds. That could be from 30-60 seconds. At the end of that period the gas valve should open, the burner should light and then the igniter will shut off. If the flame stays burning.... you're good. If the burner goes out in five seconds.... check the flame sensor.


The blower won't come on automatically until the furnace warms up.

 

So... if the burner does not light at all, then likely a gas valve problem? If it does light but then goes out in a few seconds, it is a flame sensor problem?

 

More or less..... yes. Gas valve problem or control board not sending voltage to gas valve.

 

But I have to ask: After turning the furnace on, I can see a bright orange light through the small (1") round window in the front of the furnace. The window is about eight inches right of the igniter, and doesn't give a clear view of the igniter. I'd think that it would be obvious if the burner came on (heat, sound obvious flame), but can't be certain if I'm seeing the glow of the igniter or the glow of flames.

It's tempting to just replace the flame sensor and see if that solves the problem, but here's the question: should it be obvious if the burner comes on, or could I be confusing the glow of the igniter for flame?

Thanks again. I'd love to save a service call if it's something I can manage on my own.

 

The thing at the top with the ??? is a roll out safety switch. It is ok. If it was bad the igniter would not start.

After the igniter has been warming up.... maybe 30 seconds...... you should hear the gas valve click open and then a few seconds later the igniter will turn off. At this time the burner would establish itself. You should be able to see the flames in the site glass when the burner has lit.

You have an upflow furnace and it's covered in the following manual...
.nortekhvac.com/Literature/708503a.pdf

Go down to page 37-38 and read the system operation information. Your control board will have a red blinking LED on it. That will blink codes as to status. Those codes are described here.

 

I am trying to troubleshoot my daughter's furnace, and having a similar issue. Her furnace had a motherboard issue, with no red light indicating power to the mother board, as well as a blown 3amp fuse on the board. After replacing the motherboard today, the furnace tries to go through the start up sequence, like yours. It shows the igniter glowing, and I think the gas valve comes on briefly, but it shuts down in a couple of seconds, and I get a continuous blinking led on the board. That shows in the wiring diagram as a faulty gas valve or gas valve solenoid. Strange, you photo looks just like her furnace. I guess they are all pretty similar, but even your gas valve looks like hers. Upon discussing this with a friend, he tells me that at the start of each heating season, he always has to restart his furnace several times to get it to light the flame. He also tells me that another friend of his has a natural gas fired generator, and if it has not been run in a long time, the manual says to purge the gas line, in fact, they put a manual purge valve near where the carburetor would have been. He opens it until he can smell gas, then shuts it and the generator starts right up. Stupid question of the day....does natural gas go "bad" in the line of an unused gas appliance if it hasn't been used in a long time? Anyone know? I am going back tomorrow and repeat the startup sequence several more times in order to purge the line. I'll report if it works and the furnace starts.

 

Welcome to the forums.

Similar is not close enough when servicing furnaces. They all burn gas and create heat but that's where the similarities end.

On either side wall near the burner is the ID plate. Post the make and model of the furnace.
Your problem sounds like a dirty flame sensor rod. This is a completely different problem to this post as this members burner appears to be not lighting at all.

It's pretty rare for the board to cause the fuse to blow. Usually the problem is a short in the thermostat wiring.

 

Welcome to the forums.
You should be able to operate your furnace with the top panel removed, so you can better see what is happening.
On a call for heat, the inducer blower should start. After a given period of time, the igniter will glow.
Then you should hear the gas valve click on and the burners should all light. Once the furnace reaches a set temperature, the main blower should start.

Go through the steps and let us know how far you get.

 

Thanks Pete & Woody!

I checked again, and the igniter glows, but the burner doesn't light. The draft induction motor starts, 50 seconds go by until the igniter glows brightly, there is a click, which could be the gas valve, but no flames appear in the site glass. The igniter stops glowing about seventy-five seconds after the induction motor starts, then nothing.

I also checked the manual you linked to, Pete, but wonder if it's for another unit. It doesn't look anything like my furnace, and refers to refrigerant. I did look at the control board, and see only a single, steady, red LED. I'll dig around to see if I can find codes for it online. If you do have another link, that would be great. If I find it someplace else, I'll post here for future users.

Edited: I wonder if it could be the pressure switch, since there is a click after the igniter heats, but no flames appear. That looks like the lease expensive solution, so my fingers are crossed!

 

My apologies. The manual I linked to was another unit I was working on with another member. Your manual is at the following link....

http://www.nortekhvac.com/Literature/708503a.pdf

Pages 37-38 for troubleshooting help

In looking at the schematic..... there should be a yellow and brown wire on the gas valve. You need to check these two wires for 24VAC when the gas valve should be opening. (that should be when you hear that click and just before igniter turns off.)