I have A 6 year old Heil furnace model NTC6150kj, and a couple of weeks ago I noticed my Aprilaire humidifier was running even when the furnace shut off. The humidifier will not cycle on and off as it is supposed to. During investigation, I heard a fairly loud humming noise coming from somewhere around the Fan Timer Control panel. At first I thought maybe it was the transformer or capacitor for the fan. Now I an beginning to think it is one of the relays on the fan control board. Is there any way to test this or do I just need to replace the whole board? Or could something else make the relay humm like that? The transformer is putting out 27.4 volts. The humming only stops when I turn off the power to the furnace completely. Please help. :confused:

You may have a stuck relay that runs the humidifier. You need to trace down the wires on the humidifier to see if they go to a relay or the control board on the furnace.

Thank you. Well, using your advise I checked on the humidifier operation. I found out why it was running continiously. When they installed it, they made the 120v outlet for the humidifier dedicated for this and the line voltage only goes to that outlet when the fan kicks on. There were two separate outlets and I did not know I had it plugged in the wrong one. So, one problem solved. The humming at the fan timer control board still is there and not caused by the humidifier. Should I just replace the whole board? I don`t want to wait until it is too late and the furnace totally quits. Its still very cold here in the Chicago area. Any more advise?

You might check to see if you tighten up the board a bit and see if the hum subsides. If this does not work loosen up the board a bit and see if that helps. This is a long shot because I hate to see you replace a expensive board just because of a hum.

Transformers hum sometimes because the coils assembly loosens over time. This looseness over time will become enough for the hum to take place. The stack of plates that surround the coil is what comes loose allowing the coil to become loose causing the problem.

One other trick. If there is a space below the transformer sometimes you can wedge a non metallic item like a piece of round tooth pick or plastic item under it and that will tighten it enough to stop the hum. Just a thought.

Thank you for your help HVAC1000. What I originally thought was a relay on the board turned out to be exactly what you thought. There was a vibration or humming coming from the transformer which may have vibrated the relay more then the steel mounting plate. I guess it was the path of least resisitance. The transformer actually just snaps into some spring clips which hold it in place to the metal back plate which also supports the board. The board is held in with some plastic pressure clips also, so no screws to check there. One last thing, because of the humming or vibration, does that mean the transformer is beginning to fail? This is probably the cheapest part to replace.

Transformers do vibrate. It is there nature since they are somewhat of a electro magnet on the coil end. A smart person might try to find a transformer just in case it is needed at a later date. They cannot be that expensive and you have the luxury of time being on your side.

I think I will order one to be safe. Thank you for your help. It saved me from paying for an expensive service call.