Humming Noise - Duomatic Olsen with Beckett AF Burner

[lucid]

The furnace operation seems OK, but lately I'm hearing a noise that concerns me. It's an "electric" humming sound about 20 seconds long, ending with a click that sounds like a relay dropping out.

It seems to be random, meaning that I can't relate to the burn-blower cycle, only that the "cool-down" (?) blower cycle is about the same 20 seconds in length.

Thanks for any suggestions on this.

Bruce Young in Madison NY

[HayZee518]

the noise you describe is that of a thermal overload. it is a button that contains a bimetallic strip with a set of contacts on it. the "click" is the contact set opening and shutting off the control circuit and/or the motor itself.

[lucid]

the noise you describe is that of a thermal overload. it is a button that contains a bimetallic strip with a set of contacts on it. the "click" is the contact set opening and shutting off the control circuit and/or the motor itself.

I don't think that's it, because there's nothing going on to "overload". Nothing is running. This hum occurs randomly between burner cycles -- not immediately before or after a cycle. It's just "out of the blue" during dead time. Or so it seems.

I can baby sit and time it's start, following a burn cycle if that will help. Could it be a "false" triggering of the igniters , then timing out after 20 seconds? (wild guess)

[paul52446m]

The furnace operation seems OK, but lately I'm hearing a noise that concerns me. It's an "electric" humming sound about 20 seconds long, ending with a click that sounds like a relay dropping out.

It seems to be random, meaning that I can't relate to the burn-blower cycle, only that the "cool-down" (?) blower cycle is about the same 20 seconds in length.

Thanks for any suggestions on this.

Bruce Young in Madison NY

It is most likely in the electric board. You probably have a delay on break built into your board this means that when the furnace is shut down it can take any where from 30seconds to 90 seconds for this heater switch to cool off and then it clicks off and the furnace is ready to start again upon call for heat. Usually this is silent except for the click. Paul

[lucid]

It is most likely in the electric board. You probably have a delay on break built into your board this means that when the furnace is shut down it can take any where from 30seconds to 90 seconds for this heater switch to cool off and then it clicks off and the furnace is ready to start again upon call for heat. Usually this is silent except for the click. Paul

Thanks Paul, but as I said, this humming is generally sporadic and random. It doesn't seem to happen at any consistent time, relative to burner operation. So I don't think your tip on the "heater switch" cool-off time really applies here.

I tracked it some (from upstairs) yesterday and got the following, when listening for the random 20-second humming noise.

6:12 AM, burner OFF, at end of a normal burn cycle.
6:14, HUM (always about 20 seconds long)
6:20, HUM

6:28, burner ON [been off 26 min]
6:34, OFF (6 min cycle)

6:50, burner ON [been off 16 min]
6:59, OFF (9 min cycle)
7:09, brief On-Off (1-2 min)?????

7:14, ON [been off 15 min]
7:20, OFF (6 min cycle)
7:22, HUM <===this one IS close to burner OFF time
7:32, brief On-Off

7:38, ON [been off 18 min]
7:44, OFF (6 min cycle)
7:46, HUM <===this one too, but note 6:20 above, 8 min after burner off
7:55, On-Off

8:02, ON [been off 18 min]
8:08, OFF (6 min cycle)
8:10, On-Off

8:30, ON [been off 22 min]
8:37, OFF (7 min cycle)

8:55, ON [been off 25 min]
9:02, OFF (7 min cycle)

9:26, ON [been off 24 min]
9:32, OFF (7 min plus 2 min "after-blow", strangely missing on other burn cycles)

10:00, ON [been off 28 min]
10:07, OFF (7 min cycle)

10:48, ON [been off 48 min]
10:54, OFF (6 min cycle)
Seemed to be HUM-free the rest of the day, but heard a couple this AM.
I'll try to spend some cellar time and see if I can localize the approximate area on the furnace.

[paul52446m]

Thanks Paul, but as I said, this humming is generally sporadic and random. It doesn't seem to happen at any consistent time, relative to burner operation. So I don't think your tip on the "heater switch" cool-off time really applies here.

I tracked it some (from upstairs) yesterday and got the following, when listening for the random 20-second humming noise.

6:12 AM, burner OFF, at end of a normal burn cycle.
6:14, HUM (always about 20 seconds long)
6:20, HUM

6:28, burner ON [been off 26 min]
6:34, OFF (6 min cycle)

6:50, burner ON [been off 16 min]
6:59, OFF (9 min cycle)
7:09, brief On-Off (1-2 min)?????

7:14, ON [been off 15 min]
7:20, OFF (6 min cycle)
7:22, HUM <===this one IS close to burner OFF time
7:32, brief On-Off

7:38, ON [been off 18 min]
7:44, OFF (6 min cycle)
7:46, HUM <===this one too, but note 6:20 above, 8 min after burner off
7:55, On-Off

8:02, ON [been off 18 min]
8:08, OFF (6 min cycle)
8:10, On-Off

8:30, ON [been off 22 min]
8:37, OFF (7 min cycle)

8:55, ON [been off 25 min]
9:02, OFF (7 min cycle)

9:26, ON [been off 24 min]
9:32, OFF (7 min plus 2 min "after-blow", strangely missing on other burn cycles)

10:00, ON [been off 28 min]
10:07, OFF (7 min cycle)

10:48, ON [been off 48 min]
10:54, OFF (6 min cycle)
Seemed to be HUM-free the rest of the day, but heard a couple this AM.
I'll try to spend some cellar time and see if I can localize the approximate area on the furnace.

Usually the biggest hummer on a furnace it the 120 to 24 volt transformer.
I have seen transformers hum so load that they will vibrate. When its in use the 24 volts drops down so it doesn't hum as much. The only other thing you could check is the voltage going to the unit and see if it stays steady or does it pulse some, this can make the tran. hum. Paul