I have a concord 80 plus furnace. I tried turning it on and it runs for a few seconds and shuts off. Sometimes it will ignite and sometimes it won't. I replaced the flame sensor and the pressure switch, I have sucked/blown on the tube and cleaned what the tube connects to with a small piece of wire but no luck. I also go on the roof and checked the flue or whatever the pipe is up there and it is not clogged that I can see. The LED light on the circuit board is flashing three times which should mean the pressure switch is open with the inducer on.

You will need a volt meter to confirm the switch is actually open. Do you have one & know how to use it?

You will need a volt meter to confirm the switch is actually open. Do you have one & know how to use it?

I am having the same problem and stumbled across this page. I have a volt meter and know how to use it, I just don't know how to check the switch.

Teknik:
Set the meter for AC volts. Have the furnace calling for heat & the venter running. Measure voltage across the switch. If you get +/- 24 volts, the switch is indeed open. No voltage indicates a closed switch.

Exactly what is the furnace doing? Try to be as detailed as possible.

Hey thanks for the reply. I'm not freezing or anything because the furnace is running right now.

It's weird. It will work for a month, then stop. I'll go restart it and it will do 1 of 3 things.
1. Fan comes on, no flames appear in the box, shuts off and gives the inducer on error
2. Fan comes on, Flames shoot for about a second, shuts off and gives the same message.
3. Furnace starts normally, runs 10 minutes, then shuts off.


I know it's not the air intake. That was easy to check.
I know it's not the exhaust. I popped the pipe off and just let it try to run it a couple times with no luck.
I've sucked on more hoses than I can count.
I took out the thermostat out of the box and cleaned it.
None of the water hoses are clogged
I ran the water pump a couple times by pouring water into it.

I'm not sure what else it could be. It may just be that switch and sometimes it works, sometimes it doesn't.

Grrrr. I hate intermittent problems. I'm crazy enough without having to deal with a furnace which will work just fine while I'm there but such is the life of a service guy.

It is possible there is some junk intermittently blocking the port(s) to which the pressre switch connects. I've often used a small drill bit to clean them. If it's a piece of rust or something like that, sometimes you'll just push it out of the way for the time being.

Grrrr. I hate intermittent problems. I'm crazy enough without having to deal with a furnace which will work just fine while I'm there but such is the life of a service guy.

It is possible there is some junk intermittently blocking the port(s) to which the pressre switch connects. I've often used a small drill bit to clean them. If it's a piece of rust or something like that, sometimes you'll just push it out of the way for the time being.

I may just replace the switch if I can figure it out, and I can't imagine it's that hard. The furnace is a Duquesne ,an it's only 3 years old. We've been having this problem since it's second year as far as I can remember.

99+% probablility the pressure switch is not the problem.

For anyone that comes across this post looking for an answer like I did...

Shortly after my post on Nov 12, 2013 I got the same problem again. I went down and firmly tapped on the pressure switch with a nut driver (just needed something blunt to hit it with) and it's worked fine since. I'd imagine it's a temp fix to a permanent problem, but I think I know it is the switch now.