Furnace Turns on an off over and over again

[live6969]

I have a gas furnace without a pilot light and once it has reached the desired temperature setting it will stop running (as expected) but after perhaps a minute or so it will again recycle on. It will run for another 2-3 minutes and then off then on then off all day long.

The information on the door of the furnace suggests that the flame sensor was oxidized and needed snading. I have done this with no change.

I am not in a position to call a repair company as I am currently unemplyed so any advice I can get would be appreciated.

Thanks

Brett

[Hube]

How long has this been occuring? Did this "short cycling" just happen overnight, or has there been any work or new parts put in lately? Does the heat indicator on the thermostat show an increase in the room temperature when it cycles on and off all day? What model of thermostat is it. Post info and we will advise further. Hube

[live6969]

Hube,

The thermostat is an Ultra 1000. There does not appear to be any increase in temp when the unit (Bryant Plus 90) cycles on.

The last work done on the system was an inspection in January 2003 in which they cleaned the flame sensor (as I did yesterday) and blew out the condensation line. After checking the electrical and temperature difference, they declared it to be in normal operation.

I am useless with this stuff so your advice is appreciated.

Thanks

[live6969]

More information about my problem.

There is a flashing light coding system that directs me to the problem. The lights is flashing 34. The following is taken directly from the inside cover of the furnace on a sheet covering some basic troubles-hooting.

Code 34 = IGNITION PROVING FAILURE:

Control will try three more times before a lockout occurs. If flame signal lost after trial for ignition period, blower will come on fo9 90 second recycle delay. Check for:
- Oxide buildup on flame sensor (clean with fine sandpaper) - I HAVE DONE THIS
- Proper flame sense microamps (.5 microamps D.C. minimum) - I HAVE NO IDEA WHAT THIS MEANS.
- Gas valve turned off - IT IS NOT TURNED OFF.
- Manual shut-off valve - NOT SURE WHAT THIS MEANS
- Low inlet gas pressure - DON'T KNOW HOW TO CHECK THIS.
- Green wire MUST be connected to furnace sheet metal - IT IS.
- Inadequate flame carryover or rough ignition - NOT SURE WHAT THIS MEANS.

Thanks for any advice.

Brett

[amberdetoo]

I have just woken to that EXACT problem code with myu Bryant furnace.

Did you get a solution?

quote:Originally posted by live6969

More information about my problem.

There is a flashing light coding system that directs me to the problem. The lights is flashing 34. The following is taken directly from the inside cover of the furnace on a sheet covering some basic troubles-hooting.

Code 34 = IGNITION PROVING FAILURE:

Control will try three more times before a lockout occurs. If flame signal lost after trial for ignition period, blower will come on fo9 90 second recycle delay. Check for:
- Oxide buildup on flame sensor (clean with fine sandpaper) - I HAVE DONE THIS
- Proper flame sense microamps (.5 microamps D.C. minimum) - I HAVE NO IDEA WHAT THIS MEANS.
- Gas valve turned off - IT IS NOT TURNED OFF.
- Manual shut-off valve - NOT SURE WHAT THIS MEANS
- Low inlet gas pressure - DON'T KNOW HOW TO CHECK THIS.
- Green wire MUST be connected to furnace sheet metal - IT IS.
- Inadequate flame carryover or rough ignition - NOT SURE WHAT THIS MEANS.

Thanks for any advice.

Brett

[Hube]

Make sure when you sanded the contacts there is no GRIT/dust under the terminal wires. Otherwise,it looks like the flame senser could be burnt out,OR the gas pressure is faulty (Debris). But without you having any testing equipment to check a few things out, your going to have to "bite the bullet" and have a TECH check it out. When a unit goes into "lockout" it is for your own safety, CODE 34 is telling you this, Other than for the service fee, the adjustment, or part involved should be fairly reasonable, and well worth the fix. Let us know how you make out. Good luck, Hube