How to Ignite Furnace Pilot Light

Question

I'm trying to get a furnace to blow warm air, right now its only blowing cold air. I believe the problem is that the pilot light is not ignited. The instructions on the furnace say that it is an auto-ignite. Should this be a simple 'do it yourself' fix or is it best to get someone in to do it?

Jon Holdman · Answer

If you're asking the question you probably need to call a service tech.

Most relatively modern furnaces have an igniter coil rather than a pilot.  Its a small heating element.  If the furnace is operating property, the inducer fan will start first.  It forces the exhaust out the flue.  A bit later, this coil lights up.  If its working, you'll see it start glowing.  A thermocouple senses if its hot or not, and if it is, opens the gas valve.  Sensors sense if the flame ignites.  If it does, after a few seconds the main blower comes on.

On many furnaces, there is a control board.  Its located inside the blower compartment.  There may be a small (half inch) round window.  Stick your eyeball up there and see if you see a flashing light.  These boards often have an LED that will flash to indicate the problem.  On the inside of the cover you've removed to see the burners there should be a list of the code meanings.   Common failures are in the various sensors.  These can sometimes be "fixed" by sanding the sensor or where it screws to its mounting point.

If this doesn't make perfect sense, call a repair service.

Account Closed · Answer

Before you call any one, check your circuit breakers to see if one is off. If it is, flip it on.

Check the furnace to see if it has a reset button.

CHANGE THE FURNACE FILTER. That is not a joke. A senstive furnace will stop working if air isn't getting through the filter. You'll feel real dumb if you pay a furnace tech $120 to come out and change your filter.

Jon Holdman · Answer

Since Steve resurrected this thread, another tale to add to this story.  I had notice my older furnace (we have two, one in the original part of the house, one in the addition) would cycle a few times before it stayed on.  Get back from working on a rental and the old part of the house is cold.  Cycle power on the older furnace and it lights fine.  When it cycles off and on, though, it doesn't stay lit.  Of course, its zero out that night.  Pull out the flame sensor, sand it down, put in back in, and its working like a charm.  Unlike before, it stays lit on the first cycle.

Steve Babiak · Answer

This past Saturday was cold and windy in my area, and the heat to my house stopped working.  So I did some troubleshooting.

The owner's manual for the heater described operation very similarly to what Jon wrote above.  The blower was definitely going.  I opened the outside cover of the heater, and looked through the round window to see if the ignitor was glowing - couldn't see anything that seemed to be glowing.

I found this manual that explained operation of the "glow" ignitor, and how to troubleshoot the ignitor under the "BEFORE YOU START" section:

http://www.forwardthinking.honeywell.com/related_links/combustion/glowfly/install/69_2334_glowfly_installation.pdf

I figured I'd better be certain that the ignitor's glow wasn't being hidden by anything, so I switched off the electricity to the heater and I removed the screws to the burner box taking the cover off too, and then flipped the electric switch back on.  I then saw the ignitor glow, and the furnace fired up!  Nothing really wrong I thought, and started to put the burner box cover back on; once back on the flames stopped.  Switched the electricity off again, took the cover back off, and then flipped the switch back on, and it fired up again.  Then I started to put the cover back and paid closer attention - the heater was sucking that cover back.  AHA, the air intake was now coming from the furnace room and not the outdoors.  Went outside, and sure enough the intake pipe was blocked; the wind had blown somebody's dry-cleaning plastic bag around, and my heater must have been on at that time when the wind blew it near that intake, so it got sucked in.  Lucky it was only part in, so it could be pulled out easily.

Moral of the story:  These heating systems also employ pressure sensors to determine that all is well.  When something isn't right with airflow, the pressure sensors disable things.

Jon Holdman · Answer

I've seen a repair guy sand the actual sensor, too.  His claim was it cleaned up the sensor.  Don't know if this really works, since we ended  doing a bunch more stuff before this furnace started working.

I have indeed had success with sanding to improve the electrical contacts.

Steve Babiak · Answer

Jon's "sanding" recommendation is intended to give improved electrical contact to those parts that you sand.

Richard Warren · Answer

If you donâ€™t know what you are doing, you are better off having a service tech check it out.  You can also have them tune it up so that it is operating efficiently.  Some things just arenâ€™t worth messing with.

:cool:

Steve Babiak · Answer

There are such things as pilot-less furnaces and water heaters, that are ignited by an electrical signal.  If you have one of those, there could be an issue with some of the electronics.
                    
                    If, on the other hand, you do have a pilot burning unit, then you should do a search for threads that discuss this; here's one:
                    
                    http://www.biggerpockets.com/forums/84/topics/30557-gas-hot-water-heater-pilot-light-goes-out-randomly

How to Ignite Furnace Pilot Light

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