Remove your flame sensor and lightly clean it and put it back on. Also your burner runners may need to be removed and cleaned with a razor knife. The runners are the sides of each burner with an 1/8 inch clearance to move gas from one burner to the next until the final burner lights and the flame sensor can detect heat. Check it out. Happens a lot.
Clean the flame sensor with some steel wool see if that helps . Also check the pressure switch and see if air filter is clean
SOURCE: Honeywell Gas Furnace
A Make and Model number of the furnace not the thermostat will help but I can walk you thru the operation of a typical furnace. It sounds to me that the burners are igniting properly but the flame sensor is not sensing the flame and shutting down the system. You will need to find the sensor and clean it and check the wire from it to the control board. Typically, the flame sensor is found at one side or the other of the burner box. It is a small probe that the flame hits. Depending upon your model it may have a small wire attached to it leading back to the control. Or it may be part of your auto-pilot assembly. ? At any rate, you will need to get to it and very delicately brush it off. Then inspect the flame channel. This is a trough area where the flame travels to ignite all burners. Over time, they tend to fill with rust and debris. Take a small screwdriver and run the blade down the trough. Inspect the wire that goes from the flame sensor to the control board. Make sure it is not frayed or broken or shorting out and that the connection at the board is good.
Beyond that, it's time for a technician to come.
Let us know the Make and Model of the furnace (found inside the furnace cabinet) and maybe we can help you further.
SOURCE: furnace won't stay running
1
1 FLASH
Furnace fails to operate.
• Integrated control module
diagnostic LED is
flashing ONE (1) flash.
• Furnace lockout due
to an excessive
number of ignition
“retries” (3 total)1.
• Failure to establish flame.
Cause may be no gas to
burners, front cover
pressure switch stuck open,
bad igniter or igniter
alignment, improper orifices,
or coated/oxidized or
improperly connected flame
sensor.
• Loss of flame after establishment.
Cause may be
interrupted gas supply, lazy
burner flames (improper gas
pressure or restriction in flue
and/or combustion air
piping), front cover pressure
switch opening, or improper
induced draft blower
performance.
• Locate and correct gas
interruption.
• Check front cover
pressure switch
operation (hose, wiring,
contact operation).
Correct if necessary.
• Replace or realign
igniter.
• Check flame sense
signal. Sand sensor if
coated and/or oxidized.
• Check flue piping for
blockage, proper
length, elbows, and
termination.
• Verify proper induced
draft blower performance.
SOURCE: furnace blower not working how it should
first off buy yourself a honeywell stat, in my personal opinion lux stats are garbage, I have run into so many that are bad stats !!! but as far as your fan not shuting down, sounds to me like your fan center on your circuit board is bad and will not shut down the fan when needed, you will have to replace the circuit board, as the fan center is a part of the whole of the circuit board, hope that helps
SOURCE: My furnace shuts off sometimes after the first 20-30 seconds.
The two most common reasons I have found for this are listed below. You have already addressed the third one.
1) Grounding issue. This can be difficult to find but easy to diagnose. Try using a volt meter or even just a piece of wire. Touch one end to an unpainted surface of the interior furnace cabinet and the other end to the sheet metal plenum or other ground. If the symptoms go away then you have diagnosed the problem and need to find the faulty ground.
2) Pressure in the flu. Check to make sure that the flu vent pipe is not clogged or even partially filled with debris. The small rubber hose that connects to the switch from the inducer blower motor may be clogged. Also check the orifice on the inducer motor side. You can clear this with a paper clip. Water (condensation) in the inducer motor housing or pressure switch can cause a failure too. Rarely is the pressure switch itself bad. This usually will only happen if it has been physically damaged or soaked. Best of luck.
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