# Carrier Furnace Burner turns on and off continuosly while running



## JohnH1 (Jan 9, 2009)

Kinda sounds like you may have dirty or faulty a 3 wire pilot. The pilot lights the proves and main flame starts. Then the strong draft of the main flame pulls the pilot flame away from the bymetal allowing it to cool and repeating the cycle. Has happened to me before.


----------



## SKIP4661 (Dec 3, 2008)

What JohnH1 said.


----------



## Jayenglert (Jan 14, 2009)

*Carrier Furnace*

Thanks JohnH1,

The pilot fires up and stays lit. I just cleaned it with some condensed air. It has run through 2 cycles and so far so good. You may have fixed it. I spent all day checking the thermostat, the flu damper, the filter and all the electrical. Let's hope it was the pilot. Thanks again for your time!!


----------



## Jayenglert (Jan 14, 2009)

*Still Cycling*

Well, I thought it was fixed. It fired up fine for 5 cycles but is now doing the same thing. Then Pilot lights and the burners fire up for about 10 seconds. Then the burners go out and on for 10 seconds every 115-20seconds or so. After about 5 cycles the blower turns on while the burners continue to cycle on and off until the thermostat finally turns the whole system off. Any one else have any ideas. Do you think it's still the pilot and should I replace that first. It really seems to be working properly.


----------



## Dr Heat (Jan 14, 2009)

you do not have a 31 yo super High efficient furnace. 

If it is 31yo it is not super anything 20 years is a good life for new tech.


----------



## JohnH1 (Jan 9, 2009)

Jayenglert said:


> Well, I thought it was fixed. It fired up fine for 5 cycles but is now doing the same thing. Then Pilot lights and the burners fire up for about 10 seconds. Then the burners go out and on for 10 seconds every 115-20seconds or so. After about 5 cycles the blower turns on while the burners continue to cycle on and off until the thermostat finally turns the whole system off. Any one else have any ideas. Do you think it's still the pilot and should I replace that first. It really seems to be working properly.


The only way to clean the pilot is to take apart and clean the orfice. Use a single wire from a wire brush or stranded wire to clean out the hole in the orfice.


----------



## Jayenglert (Jan 14, 2009)

*Thanks JohnH1*

Thanks JohnH1,

I'm off to bed now but will try to clean it out in the morning. Luckily the wood stove is working well and the other 2 furnaces in this house are in good working order. Wish me luck!!


----------



## Jayenglert (Jan 14, 2009)

*Still Cycling*

I just took the Pilot apart and all the burners out and cleaned them. The Pilot stays lit and strong but the burners still cycle on for 15 seconds and then off for 5 seconds throughout the heating cycle. The gas comes on and then off. Could it be the Thermostat? Although when the burners go out the Pilot stays lit. When the Thermostat turns the furnace off I notice the Pilot goes out.


----------



## JohnH1 (Jan 9, 2009)

Just to confirm this is a 3 wire pilot correct. And the only other thing I can think of that would cause this is if the pressure switch is dropping out. But sound more like the pilot.


----------



## JohnH1 (Jan 9, 2009)

One additional thing. When the main burners light up do they look low or does the pilot look to get smaller? Low gas pressure can can cause a simmiler effect.


----------



## mshaw290808mi (Sep 18, 2011)

*Carrier switch test and adjustment*

Just fixed this problem on my 1986 Carrier Weathermaker sx. I took the switch out cleaned and put it back in, did not work. I then remembered the mantra, "test like you use it, use it like you test it." I took it back out but my ohm meter across green and yellow, ground as should be. Put it across yellow and white and had an open circuit. Mounted switch in vise, hooked ohm meter up to it and heated it with a propane torch. Now had open circuit between Y-G wire and and open between y-w wire. At the bottom of the switch I noticed white cement filler in two holes, cleaned out the cement and found adjustable screws! I adjusted them so only g-y wires were closed circuit when cold and w-y closed when hot. You have to check them both, I had a case were both connections were closed when the switch was heated up with the propane torch! Test like you use it, use it like you test it. When I was growing up many times I would save money by sanding down the points on the ignition points for my car engine. When I did this I noticed that I would take it down to shiny metal but I would no longer have the protective coating that covered the points, they did not last as long as a new pair. I had to do the same with these contact points. I do not know how long they will last. Thought about putting electrical grease put the grease acts like glue that particles can stick to which will keep the points open. New switch is $133. It takes me an hour to take the switch out, clean, test, and adjust and put back in. I will see how long this switch lasts? Good luck.


----------



## mshaw290808mi (Sep 18, 2011)

*UPDATE* The furnace started to turn on and off again. I VERY CAREFULLY took of the top gas valve, AFTER SHUTTING OFF THE MAIN GAS VALVE. I found that one of the wires that controls the solenoid had broken from its solder joint, it was still touching it and the right vibration would make an open connection. I soldered it back up AND CAREFULLY REASSEMBLED it. I has been working perfectly for a week straight. Good luck!


----------

