OT: Banging from home heating/AC unit?

It's been raining and windy. Last night, right when the heating unit kicked on, we heard some very loud banging noises coming from the roof, where the heating/AC unit is located on our house. No warm air came from the vents. We shut the heater off immediately. This morning, although it is still raining and windy, we tried it again, but with the same results (banging, no warm air).

When I've done a Google search, I've not found anything that mentions "no warm air" + "banging sound" (I found numerous sites that mention the banging sound, and theories abound, but many of them have to do with condensation in the pipes/ ducts or delayed ignition).

Advice or suggestions are greatly appreciated. Are there things to check first (the one web site that suggested that it was delayed ignition said that this was a dangerous condition and that a technician should be called)? A service call is very expensive, so I'm just trying to figure out the best approach.

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More information: It's a heater/AC unit on the top of the roof. It was serviced in the summer for the A/C, and the serviceman changed the condenser for the motor and the motor capacitor because apparently the unit was not blowing cool air.

Also, my girlfriend informs me that this banging/no-heat thing has happened once before, and she simply waited until it stopped raining, and the unit worked fine the next day.

I'm in Los Angeles, so this isn't the sort of emergency that someone would have if they were, say, in Minneapolis . Also, I have a space heater. I simply can't find anything online that specifically addresses this issue, and am looking for advice. Thanks.

Well, it seems very likely from your description that the fan blower has it hitting its cage. This can happen if the bearing goes out in the motor, or if the fan blade comes loose.

Can't you go up on the roof and check it?

What kind of unit is it? Heat pump?

Terry D.

It's intermittent "banging", with a fair amount of time between "bangs". Each bang is exactly the same pitch and loudness, and it doesn't sound like something is loose. Each time, it "banged" about 3 times before we shut off the unit, with probably about 20 seconds between each noise.

I don't know what kind of unit it is, to be honest, other than it's a rooftop A/C and heating unit that's at least 25 years old.

It's raining and windy, so I'm not going to go up there right now to check!!

Thanks!

I've googled those words also and it came up with this article:

no warm air + banging sound

Don't think it helps you with your problem

Delayed Ignition is indeed extremely dangerous - - basically, there is a delay when the furnace is supposed to light, so there is gas being released into the combustion chamber during the delay. When it finally ignites, there is enough gas built up to host a small explosion. This is the 'bang' you are hearing.

The danger is that the delay will get long enough to leak enough gas to blow up the building.

My advice: Get it fixed by a professional immediately. It isn't worth dying for a $100 repair bill.

Boosh:

That link is really funny! And interesting.

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Philbo:

Thanks for the advice. We will have someone come out to look at it.

That said, now it's working. Argghhhhh. I guess now there's no delay.

Ken,

If the problem is intermittent, then that means the problem may recur at a time when least expected; possibly during the night when you are sleeping. When dealing with something as deadly as natural gas, a silent killer, the expense you'll pay to have the heating unit examined by a professional would be far less than the loss of life.

By running a furnace that you know presents potentially serious dangers, possibly even deadly, without first having the unit inspected and repaired by pros; you are compromising the safety of yourself, your girlfriend, and all others that may be in the building.

If there is even the slightest chance of there being a problem with an intermittent delayed ignition; you shouldn't run the unit until you have it thoroughly checked out by qualified technicians. To ignore the warning signs and run the unit as if nothing had happened to send up red flags; it might result in disaster. As Philbo said, Delayed Ignition is indeed extremely dangerous - - basically, there is a delay when the furnace is supposed to light, so there is gas being released into the combustion chamber during the delay. When it finally ignites, there is enough gas built up to host a small explosion. This is the 'bang' you are hearing.

The danger is that the delay will get long enough to leak enough gas to blow up the building.

If there is any chance of a gas build up, the spark created by the auto ignition ......

For your own safety and the safety of others, don't delay getting the unit serviced by pros. If you have alternate means of heating, turn the unit off entirely until you can afford the service call.

Don't assume it's working properly because it's no longer doing what it was to send up the alarm; especially since there is a history of the same problem from before.

Stay safe!!!

Ani, thanks for your concern. We're calling the technician tomorrow morning because we are also concerned (and alarmed at how loud it was!!).

So just in case someone does a search on HC to try and find out why their heating unit is making big banging sounds and doesn't turn on....

It is indeed delayed ignition.

It's dangerous for the reason Philbo said. But it's also dangerous because even when it does ignite, it's having to use considerably more gas than it would ordinarily.

Seeing as the unit is very old and in bad shape, I opted for a new unit, which will be installed next week. In the mean time, the current unit is disconnected and will no longer be used.

That's good news. Now I can tell you that one of the loudest noises I ever heard in my old neigborhood was the sound of a house 4 blocks away blowing up. Yes, it was a gas furnace. The house was half brick and it was flattened.

It is really nothing to screw around with.

There. That should keep your hand off the thermostat until they show up.

Before the guy left, I told him that I turned the thermostat off.

He replied, "Great. But it doesn't matter because I disconnected the electrical cords and from the unit itself."

He went on to explain that by law, he is required to shut the unit off due to its potential danger.

The technician said that even when the unit was "working", it was most likely requiring 6-10x more gas to finally ignite than it would if the unit were working correctly.

Given that the heating/AC unit was ancient and in very bad shape, rather than repair it and then wonder if the firebox was going to eventually collapse and leak carbon monoxide into the house, I opted for a brand new Ruud 13-SEER unit. It should be installed by the middle of next week.

santa claus is running a couple weeks late?

??

Are you talking about the fact that it's Armenian Christmas today? If that's so, then yes, Dzameer Poppy (Santa Claus) has made the rounds again.

If you're thinking that maybe one of his reindeer collided with my rooftop heating unit and caused delayed ignition, well, perhaps that's something we can discuss with the Big Guy from the North Pole.