Burner only heats for 1 min or so before blower comes on

[Shades1963]

I have a Beckett "A" "AF" series burner. I'm not exactly sure who made the furnace. For a couple years now I've had a problem with the burner coming on as normal and it will heat for approximately 1 to 2 minutes. It will then shutoff and the blower will come on and it will run approximately 1 to 2 minutes then shutoff. The burner will then come back on and heat again for another 1 to 2 minutes. It will then shutoff and the blower will come back on again for another 1 to 2 minutes. It will continue this cycle until the proper room temperature is reached.

Does anyone have any idea what could be causing this?

I found 2 silver discs I thought might be "sensors". I found one that was towards where the hot air exits and one towards the other end covered in a housing. I took these off and went to a heating supply dealer and they couldn't tell me what they were and they couldn't match them to anything they had. I ended up putting them back on and leaving it alone. I also changed my thermostat thinking maybe it could be part of the problem but it wasn't.

All responses are appreciated, THANKS!

[marbobj]

From a novice, now (but I had the same problem). It's the time limit switch. That's the little guy that lets the burners warm up to a point, then kick on the blower. Then when the sensor for the furnace insides tells the switch "it's too hot in here" it shuts off the burners and kicks on the blower to cool things down.

There could be something with the temp sensor for the burners, or something restricting the air flow for the blower, too, but this is the area you need to look at.

Ecman51 knows this stuff. He works with it all the time.

[asm660]

Sounds like a shout cycle
looking for the relay this is what your therastat wires go to is it on the burner or the smoke pipe???
William

[dun11]

I would start at the fan limit (little silver box) behind furnace door.

What are the limits set to?

When was the last time the furnace was cleaned and serviced?

[ecman51`]

It could be different things. Fire going out, then having the fan come on, til etc., etc., could be the wall thermostat opening premature, due to way low antipator(in a mechanical stat) or too often heating cycle time setting, or temp swing controls in the stat set to low like at 1 degree.

The reason the blower can come on after the fire stops is that the heat keeps building through the walls of the exchanger, then finally reach the fan limit temp sensor and kick the fan on.

There is more it could be. But I would start here, to see if the stat is short cycling.

Marbobj,

I am only a handyman, but now have built up some years tinkering with HVAC (starting 24 years ago with various mobile home furnaces), where more years back I was more into the building aspects. I enjoy the challenge of diagnosing anything. There are more actual even licensed experts here, including mods.

[Shades1963]

I think I might have solved my problem. Since my furnace is a floor furnace I crawled under the house to try and get the model and maker of the furnace. I noticed my exhaust pipe elbow was laying on the ground almost pulling it apart at the next seam. I got a block to give it support and was going to tape it up. I grabbed the exhaust pipe and went to lift it and it started crumbling in my hands. I looked closer and found that the exhaust pipe was totally deterioated. I replaced it and taped it nice and tight and it seems to work more like normal again.

I take it that all the air flowing back into the furnace was causing the problem.

Thanks for all the responses and the help!