York gas furnace P3USD12N08001B

[Susan]

My York furnace is about 18 years old and has a spark ignition.  When I'm running it, the the burner keeps cutting off then lighting back up every few minutes (the blower stays on).  This continues until the furnace shuts off once it reaches the temperature I've set the thermostat to.  Any advice?  Thank you.

Susan     

[AccApp]

Most likely an airflow issue, what is the incoming air temp? Exiting air temp? What does the filter look like? How much time for each part of the cycle?

[Susan]

The filter was changed 3 weeks ago.  When I got home tonight the temp in the house was 66 degrees, I turned the thermostat to 71.  Once the furnace came on, it took about 8 minutes for the burner to cut off the first time (blower continued to run).  30 seconds later the ignition started the burner again.  This happened another two times, about every 7 - 8 minutes, before the furnace turned off once the set temp was reach.  Could it be a problem with the thermostat? (Lux programmable) 

[hvacdrd]

Do you know if the furnace has a diagnostic light? If you are unsure, is the furnace in a basement, attic, closet, or do you know if it is an upflow or downflow? (This information will help me point you to the location of the control which typically has the diagnostic light)

[AccApp]

It is not the thermostat, the furnace has built-in protection devices to insure safe operation. Without knowing the incoming and exiting temps it is not easy to guess but I would say you don't have adequate airflow for some reason. Most often the blower wheel gets clogged with dirt and fails to push enough air through the unit. Could also be the A/C evap coil is clogged. You'll have to start digging around and see what's up.

[Pegi]

We had a problem with our central furnace doing what I called "short cycling" a couple of years ago, would start the start up sequence then stop, then restart, burner may or may not come on then it would shut down again...was found the board that controls this had cracks in the traces...replacing the board solved our problem...this might be something to look at if yours has a control board...believe ours is Carrier but this might apply to any that have a control board.

[Guest ahammer48]

Hello

There could be several reason why this is happening. It would be helpful to know approx how long the cycle period is, on/off.  Do you C the spark ignition control board (or box), and do you C the wire going to the spark ignitor? Usually it's a orange wire, heavy insulation. Looks like the spark plug wire of your car. Is it easy for you to C the burner manifold? (where the flame is)

Make sure the unit is off when you look around (unplug it). If you C the spark ignitor can you see another probe (flame sensor), most likely, (but not always) mounted on the opposite end of the burner manifold. It will also have a wire coming from it and going back to the control board.

If you have a flame sensor, first thing you want to do is inspect the wire. Make sure its not cracked, broken, etc, and attached securly at both ends.If that checks out what you want to do is get a telescoping inspection mirror-auto supply store. With the unit running-this isn't dangerous- use the mirror to C how much of this sensor is in the flame, with the unit running. C if the flame is being blown away from this sensor. 

At least 1/4-1/2 inch of the probe should be exposed to the flame. Make sure it is not touching the metal of the burner manifold. Watch it untill the cycling starts. I've seen these probes heat up and bend due to the heat and short to metal of the manifold.

In some furnaces the spark ignitor also doubles as the flame sensor. If you only have one insulated wire, then thats your furnace. You need to do the same checks as above.

You may have a high temperature limit switch thats opening up if the cycle rate is like 5 minutes. Do you believe that you have a good amount of air coming out of your vents or is it just so-so? Some of the older furnaces used a fan belt to connect the fan motor to the blower. If its loose then your not moving enough air and the limit is tripping.

Make a couple of checks if you can get to the blower section and burner sections and let us know what you C. Just be careful!!!

Hope this helps:)

 

[Susan]

Thanks to everyone who replied.  Ever have one of those moments when you feel really stupid?  I'm having one now.  A few months ago the drain pipe that comes out where the coils are was plugged, and water was running down below the furnace/blower.  So I put a heavy plastic sheet weighed down with bricks underneath.  Didn't take it out though once the drain problem was fixed.  When the light bulb over my head finally lit the other night, I thought maybe that was the problem, so I removed the plastic & bricks and everything seems to be working normal now.  I've got someone coming out to check it over in a few hours to be sure.

I'll keep these replies in my home maintenance file in case of future problems.  Thanks again!

  :withstupid:

[Guest ahammer48]

:)