Hello. I have a furnace that I can hear the following steps:
1. thermostat clicks to turn on furnace
2. the furnace immediately turns on the exhaust fan
3. then I hear a click, and the burner is burning, but only for 5 seconds or so and stops.
4. then another click, and another, etc.
5. the burner kicks on again for 5 seconds or so and stops.
6. then another click, etc.
7. the burner kicks on again and stays on this time.
8. 30 seconds later the blower kicks on and heats the house just fine.

This is the sequence, and the amounts of time it actually burns and stops varies. Sometimes it works perfectly. What could be the problem?

Thanks,
Dan

Clean the flame sensor

Clean the flame sensor

Looking at the manual, there is no "flame sensor". Here is a list of items in my furnace, maybe one of these are the flame sensor?

Switch, aux limit
Control, fan timer
Control, module
Transformer
Capacitor
Pilot/ignitor natural
Pilot orifice
Tube, pilot
Valve, natural
Switch, limit
Tubing, silicon 24"
Rollout switch, limit - there are 2 of these
Switch, pressure

Exact brand of unit?

Exact model number of unit?

It's a Comfortmaker.

It has two models listed on the same sticker:
Model NTG3050FBA4
Model FBF050B12A4

I think I found the part online: International  Comfort Products Parts (http://www.arnoldservice.com/international__comfort_products_parts.htm)
It's called the Ignitor-Flame Rod, but the manual I have does not list that at all.

This part costs $60, so I'll try cleaning it first. What is the proper way to clean? Emory cloth? Soap and water?

Thanks for your quick response.
Dan

Steel wool or fine sandpaper

So I I finally got around to cleaning the flame sensor, and it's still doing the same thing. This time was at the unit with the cover off observing. Here is what is happening...

1. furnace turns on, exhaust turns on
2. the pilot attempts to light and fails several times, then lights.
3. then the gas is full on and flames full on, but only for about 3-5 seconds and turns back off.
4. then the pilot attempts to light and fails (no flame)
a. gas turns on for about 1 second (no flames) and stop
b. the pilot attempts again and fails (no flame)
c. gas again for about 1 second (no flames) and stops
d. pilot lights
e. flames full on but only for 3-5 seconds and stops.

This cycle repeats over and over until finally it just stops. Then about 5, 10, 15 minutes later it attempts again until it eventually stays on.

I definitely see that the pilot doesn't light when it is supposed to, and when everything appears to be working it stops after 3-5 seconds. I assume it could still be the flame detector?

Maybe I didn't clean the proper area. I simply cleaned the thin rod that has a single blue wire going to the control module (that says "spark"). I didn't clean any other part of it.

What would my next steps be?
Thanks!
Dan

Here is my furnace...
http://icpindexing.mqgroup.com/documents/086477/44103260900.pdf

I cleaned the thin rod (bent 90 degrees) of part number 11.

Dan

Test flame rod with meter. Use this reading for test UNLESS the service manual for your unit says different. If you have the Honeywell style falme sensor ignitor combo it is tuff to clean without damaging the ignitor. Clean well BUT becareful you do not want to mess with the part that glows since it is sensitive to the oils on or in your fingertips. Clean metal rod flame sensor only.

This is not the same señor I have. Mine doesn't have a glow igniter; it is a spark igniter and sensor all in the same piece. Will I blow up my meter when it sparks if I connect it like it shows in Doc1?

Here is a link to the Sensor I have:
1011483 Pilot Burner Target Intermittent Ignition (http://www.allpartsheating.com/1011483.html)

I just learned how to add a picture to a post. :-) Here is the sensor I have...
29780

You do have the old style spark ignition. Those systems require a good ground so what you are saying is that it sparks and lights off the pilot but then turn right off? Post the brand and model number of the control the blue wire plugs into.

It takes about 3-6 times before the pilot lights, and when it does, the burners will start to burn but only for 3-5 seconds, then they stop.

The control module is Honeywell. Here are the numbers on the side of the unit:
S8600M 105(1)
HQ1011449HW
0012 M

Look over this. It has a trouble shoot section etc. Make sure pilot orifice is not restricted and enough gas leaves pilot to sustain the pilot light. Then go step by step in manual till problem is found.

http://customer.honeywell.com/techlit/pdf/PackedLit/69-1954.pdf

The problem is solved. Just wanted to give an update. I took a look at the document you showed and it was good, but it wanted me to test the pilot and remove the MV wire, but mine is on a harness of 3 wires and the other side had 2 wires. I attempted to pull the harness, but that didn't allow the pilot to light. The grounding was good; tested with ohm meter and reseated the connections anyway. The way I saw it, I had two options; replace the igniter/senor or the control module. The igniter/sensor seems like the best option and it was cheaper. It came in today and it fixed my problem.

Thank you for your help.
Dan

Many times you need a manual for exactly what you are working on to really understand all that goes on. Glad you got it going.