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This actually just started a day ago and I am trying to figure out as much as I can before calling a service person (if necessary). My apologies in advance if I am leaving out important details but I've never dealt with a faulty heater or A/C before.
My central heater in the attic was running for about 5 hours on Sunday morning according to the thermostat log but the house was quite cold that morning. When I tried to manually get it to turn on, I could hear it make a humming noise like it usually does when it starts and about a minute later the air started blowing. Unfortunately only cold air was coming out and after a few minutes the whole system turned itself off. So being curious I climbed up into the attic, read all the warnings on the outside of the unit, and proceeded to remove a few panels and look around. I did flick the on/off switch to the off mode for the outlet connected to the unit although I imagine the main breaker was the place I really should have turned off. I did not touch anything inside since all the "explosion" warning on the outside scared me half to death. I'm glad I read all the warnings about not potentially igniting gas with flames since I had gone up carrying a lighter thinking it was the good old fashioned piloted furnace (obviously not).
So now, after doing a few simple searches online, I am wondering if this is an ignition switch issue? Or a circuit board or fuse burned out? We were getting good heat until yesterday and now this happened. Now I'm losing sleep over how much this potentially might cost us.
One other note, when I opened the panel in front of the fan (between the intake vent and the part leading to the burning chamber) and found what looked like a loose sheet of filter material on top of the fan. From the adhesive backing, it looks like it was supposed to be attached to the ceiling part of the chamber but had fallen on top of the what appears to be the intake side of the fan. I removed it since it looked old and dirty anyhow.
I'd appreciate any advice or suggestions. I'll probably put out a service call this week but any insight would be great.
I agree it most likely is more complicated than I can handle and I have no intention of putting myself or family in risk. But I thought I might get some idea of what is wrong from those who have more experience with this than myself.
I generally prefer not to go into any service call (automotive, etc) completely blind. But if you think this is something far more technical than you can understand then it definitely warrants an expert.
I hope it is warmer where you are than here, below 10 F this morning. With all the scary warnings today, it is a wonder anybody survived before we had them all.
Most modern furnaces follow this cycle. When the thermostat switches the power to heat, the gas ignitor comes on and heats up. Once it has had time to heat up, the gas valve opens and the combustion air blower starts. If the gas doesn't light almost immediately, the gas valve shuts off. It will try again soon if not. If it does light, the blower will come on soon, usually after a limit switch heats up, but yours must be timed. With a panel off, you could observe a cycle. You want to be able to see the burner. Locate the ignitor first. It will be a little loop or spiral of metal near where the gas comes out. Start a cycle, perhaps by pushing the switch that shuts the power off when you remove the panel. That switch is there to protect you. Do not touch any electrical terminals while holding it shut. See which step in the above sequence fails. The ignitor should get red hot, then you should hear the gas valve click open, smell gas, and the gas light. The gas valve is the box with wires between the gas pipe and the burner. If the ignitor fails to heat up, it may be bad. You can remove it and take it to a dealer for your brand of furnace and buy a new one. Before replacing it, check to see if it is getting power if you can. If it isn't getting power, replacing it won't fix the problem. Measure the resistance between its terminals if you can. If it is open, it is bad.
If it is heating up, and the gas doesn't come on, either the gas valve is bad, or the control board is bad. Many of the problems are components on the board, tough for the DIY to find and fix. Often as not big bucks for a new board because a cheap little relay died. Circuit boards aren't that bad to replace, but I hate to tell people to replace expensive parts if they can't be sure it is the problem.
One last thing. Do you have any other gas appliances, and are they working? The furnace will not work if it isn't getting any gas. You don't want to pay a HVAC tech to tell you that you should have called the gas company.
Thank you, Labman. Just the response I was looking for.
All gas appliances throughout the house are working fine so I don't think it's the gas. I have read many of your past responses to others (very helpful I might add) but I find it odd that in my case the blower is going for about 3 or 4 minutes until it seems to figure out that is blowing cold air. Then it finally shuts itself off. In all the other examples I have read about this normally should not happen: If the ignitor does not light, it should be smart enough not to force cold air throughout the house, right? But strangely it seems to realize it is not working after a while THEN shuts itself off the blower.
Unless I am missing something blatantly obvious and simple, I'm going to make that call although it'll probably be days until someone can come.
So service was done and turns out the ignitor was burned out. Simply its normal course of life. I checked on-line: the ignitor is about $30 plus $5 shipping. I paid over $230 for the service call (parts, labor, diagnosis) but I realize that's the price of 'expertise'. However, I intend to now always keep a new one of these things around. After turning all the power off it does not appear to be too difficult to replace the ignitor. Apparently a normal life of 2 to 4 years is not unusual.
Thanks for your previous advice. The HVAC tech did point out some other service issues so I don't feel the visit was wasted.
If you do buy an extra igniter be very careful with it. They are fragile and also never tough the carbon part of the igniter with you fingers. The oil in your fingers will shorten the life of the igniter dramaticly........Another possible problem that you may have had is your flame sensor...it looks like piece of hard wire that is in a position in front of one of the burners. If you furnace comes on and it does not detect flame it will cut your furnace off and start the cycle again......this will happen for about three times and then your furnace goes into lock down and the only thing that will run is your blower motor in your furnace. The Flame sensor can be cleaned with some some sand cloth or light sand paper. It is easier to remove the sensor to clean it.
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