Originally Posted By: poffenberger This post was automatically imported from our archived forum.
inducer runs for 60 seconds ,ignitor comes on, main flame lights for 6 seconds then goes out… again same sequence…but main flame stays on for 120 seconds and then shuts off and house fan and or blower comes on and stays on … what do ya think
Originally Posted By: Blaine Wiley This post was automatically imported from our archived forum.
Possibly a bad flame sensor. And…
"Furnace was not operating properly at the time of the inspection. Recommend a more thorough diagnosis and repairs by a qualified licensed HVAC contractor".
Originally Posted By: kleonard This post was automatically imported from our archived forum.
bwiley wrote:
"Furnace was not operating properly at the time of the inspection. Recommend a more thorough diagnosis and repairs by a qualified licensed HVAC contractor".
That's perfect..
I ditto Blaines response..
Kevin 
Originally Posted By: rpalac This post was automatically imported from our archived forum.
I take it your trouble shooting this for your self to learn what the problem is. Not for a report but to solve the problem.
The sequence sounds normal with the flue inducer fan and the igniter time frame.
It sounds like the re might be a safety kicking the flame out after six seconds. Some units have a roll back or role out safety the detects heat outside the chamber. If the flue is blocked, negative air pressure, or a split heat exchanger, thios could happen. The burner flame doesn't stay in the path it was intended for an rolls out toward the front hitting this thermal safety and then cuts out the gas valve.
That's a guess but not sure.
I thought that logic would point to the gas valve, temp sensor, safety, or possibly a bad thermal couple.
The themal couple is the cheapest thing to replace.
I'm curious to know the answer. Please re-post or e-mail me when you figure it out.
Originally Posted By: rsummers This post was automatically imported from our archived forum.
I have to agree with Blaine its probably the flame sensor shutting it off. The circuit board should be giving you a fault code that might point to the problem. It is out of the scope of an Inspection to trouble shoot the Furnace even if you know what you are doing and the fault codes wont tell you exactly what’s wrong.
Originally Posted By: rsummers This post was automatically imported from our archived forum.
Most of the more modern furnaces don’t have Fan limit combination controls. They do have a main limit switches , roll out switches ,pressure switches and secondary limits in the blower compartment. If the limit switches or roll out switches are open the fan will run continuously and it wont respond to a call for heat or any thing else. The fans on most new furnaces are either timed on unless the thermostat calls it 1st. Depending on what board the unit is using after a couple failed attempts at lighting it will go into a lock out and the blower will come on and some times not shut off until the board is reset. I would check and make sure the unit has a true earth ground that can cause the flame sensor problem.
Originally Posted By: wwarner This post was automatically imported from our archived forum.
I just heard from a friend had the same problem.
He had a programmable thermostat (newly installed), thought it might be the battery. He replaced it and the furnace functioned correctly for about 45 minutes, then started doing the same thing again.
So he went out and bought the cheapest thermostat he could find, and bingo, problem solved.
Originally Posted By: kluce This post was automatically imported from our archived forum.
I agree with a lot of the info before. One other possible answer is a crack in the heat exchanger. When I was an HVAC tech., I ran into a few furnaces that had cracks in the heat exchanger. Because of the location of these cracks, the flame pattern would be normal until the crack opened up from the heat. The flame then rolled back and shut the furnace down. The flame was a lazy roll back. These were on 80 plus furnaces and were about 10 to 15 years old. Most cracks were on or by the seams of the heat exchanger. Of course, this is for your information because you always want to recommend further evaluation by a licence heating tech.
Originally Posted By: gbeaumont This post was automatically imported from our archived forum.
Hi to all,
a good friend of mine has just had the same problem with flame "roll out" and the cause is probably a cracked heat exchanger, anyway the unit is being swopped out today, and later this week I am going over with a camera and a sawzall to do a bit of disection, watch this space for pictures at the end of the week  
