Furnace Question

[steveh_131]

Hey HVAC Fellas, I've got a question for you.

So far Google hasn't been hugely helpful with this. My furnace kicks on and the blower stays running. However, I can hear it trying to light and then I can hear the flame go out. It seems to do it about once a minute. I'm not getting any warm air from it, but the blower doesn't shut off (It is set to 'auto' on the thermostat').

Now, if the blower was cycling, I would think it was a thermocouple or flame sensor or something. But since the blower stays on, I'm a little stumped.

My best guess is a bad circuit board. What do you guys think?

It's a goodman unit.

Thanks!

 

[steveh_131]

Oh, and one other thing. If I turn the heat off for a few minutes then back on, it works fine for a while. Then it'll start acting up again by the end of the day. It's working fine right now.

I'm going to try to see what blinking light pattern I get when it acts up again I guess.

 

[churchmouse]

OK.......diagnosing on the internet.

The blower stays on as there is a fault of some kind.
There is a peep hole on the door to the blower.
There is a light visible inside the compartment. It is on the circuit board.
Locate that light. It will most likely be blinking. Longs and shorts. Example...3 shorts blinks is a "3"...2 longs and 3 shorts is a 23 code.
Find the chart for the codes. It will be close to or on the wiring diagram. Find your number and it will tell you what is wrong.

Do a hard reset.....main power off for 30 seconds or more and then turn it on.
It will most likely got through a 90 second power failure restart. Then it will try and start.
If the flame lights off and runs for 5 seconds and shuts off the flame rod is dirty.
It will need to be pulled and cleaned with scotch brite. Then put back in the unit.
Hard restart and see what happens. If the flame failure repeats the board is not seeing the flame.

The main blower will run constantly to indicate there is a problem

Hope this helps.

 

[churchmouse]

Oh, and one other thing. If I turn the heat off for a few minutes then back on, it works fine for a while. Then it'll start acting up again by the end of the day. It's working fine right now.

I'm going to try to see what blinking light pattern I get when it acts up again I guess.

The flame rod is dirty. Simple as that.
It is in the burner area. 1 single white (maybe) wire attached. It is a 1/16ths inch steel rod. About 2 inches long.

 

[steveh_131]

Thanks, CM. You're the man, as usual.

 

[churchmouse]

Thanks, CM. You're the man, as usual.

Well, in these issues maybe.

When you find the flame rod and get it out be careful if the unit has been on line. It will be stupid hot.

Use red scotch brite.

 

[ChristianPatriot]

Flames carrying an electric signal still seems like some kind of voodoo to me.

 

[steveh_131]

Well, in these issues maybe.

When you find the flame rod and get it out be careful if the unit has been on line. It will be stupid hot.

Use red scotch brite.

I found it, it's definitely hot. I'm going to wait for it to cool and clean it and report back probably tomorrow.

 

[churchmouse]

Flames carrying an electric signal still seems like some kind of voodoo to me.

Years ago working on main heating plant boilers I was amazed at the concept.
The combustion process of gas carries solids. These solids act just like water conducting current.
They pass a micro amperage current through the flame. If the burner is properly grounded the board will "See" it and keep the gas valve open.

 

[churchmouse]

I found it, it's definitely hot. I'm going to wait for it to cool and clean it and report back probably tomorrow.

Yup.....it will be hot.

 

[ChristianPatriot]

Years ago working on main heating plant boilers I was amazed at the concept.
The combustion process of gas carries solids. These solids act just like water conducting current.
They pass a micro amperage current through the flame. If the burner is properly grounded the board will "See" it and keep the gas valve open.

Oh I understand how it works. Still feels like witchcraft.

 

[churchmouse]

Oh I understand how it works. Still feels like witchcraft.

Voodo man.....it is Voodo.

I knew you did I was giving a -CM- Tutorial.

 

[Leo]

Oh I understand how it works. Still feels like witchcraft.

The electrical connection on the flame rod is not something you want to get your finger on while it is running. A lot more than a tickle on that wire. I have never measured a home unit, but the Honeywells in commercial stuff is over 400 VDC.

Anything that throws you back when you touch it can be considered witchcraft.

 

[ghitch75]

bad earth ground will drive flame sensing equipment crazy......specially in old house with old 2 wire wiring......i have had to drive a ground rod for the furnace alone to get it to run.....