Another Furnace Not Starting....

[1victorianfarmhouse]

I have two furnaces in my old (1895) house. The older furnace,in the basement has been a source of aggravation for a while, but is currently operating like it should. The newer furnace, in the attic, is dated 4/23/2005. It is a horizontal Luxaire, unit model gm8s080a12uh11b. It has suddenly developed the nasty habit of not starting. I have followed the instructions on the side, but it will not start (means will not ignite) and when I look in the viewhole on the side, all it shows me is two red leds inside blinking. Any comments? Yes,the gas bill has been paid...

 

[Jeff Handy]

The leds might be flashing an error code.
Look up your manual online, there might be a chart showing what the flashing means.

Obviously, you should also try unplugging it from power, or turning off the breaker or pulling the fuse.
For about half an hour.

That might reset the error code and fix everything for awhile.

 

[1victorianfarmhouse]

Thanks, Jeff! I did as you said, no change, but now I have one red LED that blinks three times, then is dark before blinking three times again. Time to look for the manual online as you said.....

And here is what I found at weinstallca:

3 RED FLASHES: This indicates the normally open pressure switch contact did not close after the inducer was energized. This could be caused by a number of problems: faulty inducer, blocked vent pipe, bro- ken pressure switch hose or faulty pressure switch.

Now I have more things to learn about and check...

Thanks!
Vince

 

[Jeff Handy]

Sounds like a safety is keeping the furnace from starting.
You must have a pvc exhaust with a blower.
Make sure the outside intake and exhaust pipes are not frozen over or knocked loose.

 

[Jeff Handy]

Three suggestions:

Kill the power to the furnace for a full day, then restore and see what happens.

Check the furnace filter or air cleaner for blockage.

Call the manufacturer customer service or tech help number for advice, they may have tips not found in the manual.

Meanwhile, if the problem turns out to be a dead exhaust blower, you could likely replace that yourself if you are handy.

Pressure switches are trickier to test and replace, leave that to a pro.

Could also be a bad igniter, some are easy to change, some are real bitches.

For grins, if you can see the shaft of the main furnace blower motor inside of the furnace safety covers, see if you can spin it.
That might unstick it for awhile.
This is probably not the problem.

If you hear the exhaust blower that is attached to the pvc vent pipe running briefly, then stopping, mention that to manufacturer help line.

Also, some furnace access doors and internal covers have switches that kill the furnace if they are not properly shut.
And the switch contacts can get knocked around, so make sure all the access covers are making contacts with their safety switches.

Check the batteries in the house thermostat, if it has batteries.
It might be that simple, but probably not.

 

[bud16415]

I had the same problem a couple years ago. Called the repair guy and he said I will be right there. 20 seconds later the doorbell rang and he was standing in my porch. What were the odds he was driving by my house when I called.


He went down to the basement and when the furnace tried to start he taped on the pressure switch with a screwdriver and it fired. He left and returned with the part in about an hour.


As I understand it the exhaust blower kicks on and is held on for a short time by a timer, during that time the pressure of the airflow a little bit of it is sent down a little clear plastic hose and trips this safety switch once that switch is made it locks out the timer relay and allows the furnace to run. The idea being if the large exhaust blower that sends the gasses out of the house fails the furnace wont come on and gas you. The little flapper in this switch gets worn or gunked up and sticks. If you are hearing it trying to start that’s where I would look first.

 

[user 4883]

Problems I've had with attic installed units is that any hose/pipe with condensate in it tends to freeze up and prevent the unit from starting. Check you pressure switch hoses and condensate hoses for freezing.
Had to wrap them with heat tape to fix the problem.

 

[1victorianfarmhouse]

Thanks for all the great info! I'm sorry I wasn't able to get on last night. Came home from work yesterday to find the furnace working like it's supposed to. It's behaving tonight, too. Temperature outside has been in the upper 20s/low 30s the past few days. I like the idea of cleaning out the switch and wrapping hoses with heat tape to keep them from freezing when it gets below freezing.

 

[Fireguy5674]

Most of those switches are on the suction side of the power vent system. They are fairly sensitive. Normally they are part of a chain of safety switches that all have to be satisfied before the gas valve will open and the burner lights. I have never seen one where condensate freezes and prevents operation, but I could see that happening. Those switches do not go bad often but they do fail. There is a pressure rating on the switches and they must be replaced with the same rating to maintain safe operation of the furnace. I had a unit that had run for several years and suddenly would not light. The code said it was a pressure switch problem. I replaced the switch and the furnace ran fine. The next heating season the unit failed again for the same reason. I finally took the vent fan out and found the seal behind it was just slightly off. I repositioned the seal and put everything back together. As far as I know it is still running. I am not saying you have that problem, but it is an example of how touchy they can be. If the vent fan is not moving enough exhaust through the vent piping that switch will not see the required suction to stay closed and allow the furnace to start or remain operating. I have seen sagged vent piping holding condensate which restricted the exhaust enough to cause a furnace to shut down, especially when it gets colder and the furnace is under heavy load.