Furnace inducer fan runs but won't ignite


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Old 10-21-16, 08:49 AM
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Furnace inducer fan runs but won't ignite

Hey all, having an issue with my Tempstar 80afue, propane furnace. I bought a home that it pre existed in in 2014. Was told the furnace was installed around 07-08. The furnace worked fine for the winter of '14 and '15. Early spring 2016 it was still a bit chilly (upstate ny) so i just let the tank run till empty through spring. So now its october and its cooling down again, i had the gas company come fill my tank.

I went to start my furnace up and noticed it didnt kick on. So after inspecting the furnace for 5-10 min i thought maybe the gas guy forgot to open the valve on the tank. Sure enough he did forget. So i opened it up, but the furnace still wont work.

The thermostat calls for heat and the inducer fan kicks on. But then it just powers down and i get the 3 blinking lights indicating a stuck open pressure switch. I start it up again and this time i lightly suck on the hose to the pressure switch and it lights right up, removed my mouth from the hose and it shuts down. I checked the flue vents and they are clear. Even disconnected the flue from the furnace and it still wont start. It has a new filter in place. I checked the port to the inducer fan and the paper clip made contact with one of the fans blades so that seems clear.

I borrowed a digital Manometer from a buddy and connected it to the inducer. It was slightly fluctuating between .37-.46 in-wg. So the inducer is drawing in some air. Maybe just not enough to close the pressure switch? The fan seems fine. I can see down into it and it seems clear and clean and uninhibited.The hose connecting the switch to the inducer isnt clogged or cracked that i can see. I hear the pressure switch usually is indicating a problem and is rarely the problem. But what do you guys think? I dont know what else it could be. Thanks in advance for any help.
 
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Old 10-21-16, 09:32 AM
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Welcome to the forums.

A typical problem is the tiny hole in the port on the inducer blower gets plugged.
It needs to be cleaned out with a drill bit, paper clip or something similar.

You'll notice the hole inside the port is extremely tiny.
You must make sure you clean thru that hole into the blower itself.

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Old 10-21-16, 10:10 AM
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Thanks for the response. If i take a paper clip and stick it in there it goes right through and touches the fan blades. Could it just be that it is clear but just not clear enough? So its reducing the suction and therefore not causing the pressure switch to close? Ill be home in an hour and ill try to clear it a bit more. Any other ideas if it doesnt work?
 
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Old 10-21-16, 12:40 PM
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PJ Max correctly suggested a common problem that can cause the condition you have. And it sounds like you checked and cleared that correctly.

Unfortunately, MANY different issues can cause the pressure switch to fail to close.

The pressure switch checks to verify that the ventilation of combustion air INTO the furnace, to burn the gas and to expel those combustion gasses out the vent are all working properly.

Disconnect the vent pipe from the furnace temporarily to see if the burners come on ----the vent/chimney may be plugged up.

Remove the inducer motor assembly from the furnace ---usually easy to do by removing three bolts or so. Inspect the inducer motor fan to see if it has broken blades or needs to be cleaned. Verify that the inducer motor fan turns freely and comes up to the normal operating speed.

Check the bottom of the heat exchanger visible through the hole for the inducer motor assembly. Look for accumulations of water, junk or debris.
 
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Old 10-22-16, 09:48 AM
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So its starting to get just a bit too chilly up here, on Monday i was going to call for furnace repair. But i decided to check the furnace one last time. Ive been messing with it for about a week now and couldnt figure it out. The vents were clear, some air was getting to the pressure switch just not enough it seemed.

Well i finally took all the exhaust pipes off and looked down into the fan (as i had done before, just not as thoroughly). Sure enough some birds feathers were deep in there. So i tried to vacuum them out, with no luck. So i took the fan off. A bird had fallen into my chimney and walked his little self right down into my inducer fan. Removed the bird, re-attached the fan, works like a charm. Thanks all for the help!
 
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Old 10-22-16, 10:22 AM
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We've recommended checking like you did but people have told us that animals could not possibly get in. You've seen otherwise now.

Thanks for letting us know how you made out.
 
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Old 10-22-16, 06:45 PM
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I am having the same pressure switch error code but everything I have tested is working properly. The inducer motor comes on before I get code 31 for a Payne furnace but I have checked the flue pipe and there is no blockage there. So I put a multimeter to the pressure switch without the inducer motor running and it shows no continuity but there is continuity when the motor is running. After seeing that I tried bypassing the the switch altogether just to see if the ignition would start but the control board still gives me code 31 pressure switch stuck open or closed. Does that mean a faulty control board? I'm out of other ideas on this one. Thanks in advance for any help.

Aaron
 
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Old 10-23-16, 01:41 PM
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>


Many circuit boards will detect the difference between a pressure switch that doesn't close after the inducer motor starts, and a pressure switch that is closed when the inducer motor is off.

Bypassing the pressure switch isn't a useful diagnostic strategy with that kind of board.

>


This is the key test, which you already made.

When the thermostat calls for heat, the circuit board turns on the inducer motor.

When the inducer motor comes up to speed, the pressure switch closes.

When the pressure switch closes, the circuit board should turn on the hot surface ignitor.

After the hot surface ignitor heats up for 30 seconds or so, the circuit board should turn on the main burner gas and the main burners should light off the HSI.

You need to check to see if the HSI is burned out. Often there is a visible crack in the HSI, or you can use a multimeter to see if there is continuity through the HSI.

If the HSI is good, use your multimeter to see if 24 VAC is being switched on by the circuit board to turn on the main burner gas.

You probably have a bad HSI, and if not a bad circuit board.
 
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Old 10-24-16, 12:40 PM
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Furnace only ignites when sucking on pressure switch hose

If I disconnect the pressure switch hose from the Inducer motor I can get the burners to ignite momentarily until I stop suction then the burners go out; the Inducer motor continues to run. I tried swapping out the Pressure switch with my other HVAC unit in the attic (which works fine) and no change; so I presume the pressure switch is fine. I then disconnected the vent tube to the inducer motor and no obstruction was found. I'm at a loss; at the end of last winter the heating worked fine; during summer the AC worked fine; change filters regularly so they're OK. Before I call a technician, I am appealing to the forum here for some help to troubleshoot further.
 
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Old 10-25-16, 12:43 PM
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I recommend that you start a new thread rather than reviving an old thread.

It's confusing to deal with threads with several different issues, and you will get better and more accurate advice by starting a new thread.

Picking an old problem someone else has had implies that you have accurately diagnosed the problem yourself---- but that is the exception.

We may be able to help walk you through a diagnostic process that will accurately identify the issues with YOUR furnace. That's the right we to go!
 
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Old 10-25-16, 05:45 PM
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Welcome to the forums. Check the exhaust piping, especially where it exits the house, for a clogged pipe. Bees and even dead birds have been found blocking the pipe. That would prevent the inducer from moving enough air to trip the pressure switch.
 
 

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