Furnace Ignition Problem


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Old 11-02-02, 09:50 AM
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Question Furnace Ignition Sometimes

Ok, here is the set up, Trane furnace XE80, model TUD100C945B0, MFG 09/94,
Natural gas fired.
This system has a fresh air intake from outside of the house to the cold air return, (gives new meaning to the word cold air return). You will see what I mean later.
New parts include Glow igniter, Flame sensor, and programmable thermostat last season.
The problem, everything starts well, the exhaust fan starts running, the glow igniter comes on, gas valve opens, flame starts across the burner assembly, (5 ports) gets about half way to the flame sensor, gas valve shuts down. Everything keeps running tries again to light this time it will work, burners light, the house get warm, all is well.
Sometimes it will even light on the first try, the problem is when it doesn’t light after the second try, the blower will come on and with that fresh air intake to the outside air, the house gets cold quickly, plus the blower keeps running bringing in all that cold air, I have to turn off the power to reset everything to start the cycle again.
Do I need to adjust gas pressure? Do I need to replace the brain box?
Thanks in advance for your help.
 
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Old 11-02-02, 11:49 AM
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Hello comtnman. Welcome to the Heating & Cooling forum & our Do-It-Yourself Web Site.

Could very well be a restricted connection port between the burners. Connect ports or slots allow the burner flames to lite between themselves. Meaning one burner lites another. Any blockage or restriction in those ports or slots etc can cause the type of problem your describing.

Cleaning these cross between ports and or slots etc should correct the problem. For more detailed information etc. read the recent postings within this forum pertaining to heater topics. The questions already asked describe like or similarly related problem descriptions as your question.

These prior postings and any or all the replies offered within them contain almost all the required information needed pertaining to the many potential and or possible problems with the heating unit your describing.

FYI Note:
This is one of several reasons why manufacturers now put flame sensors on the opposite side of the ignitor. If the burner flames fail to lite quickly and completely across all the burners, the process is shut down to avoid delayed ignition.

For the purposes of understanding the meaning of delayed ignition...Delayed ignition is that BOOM heard upon ignition....

The fan, in this case with your heater, is not operated by temperature. The fan on switch is a TDR. Tdr is Time Delay Relay. Which simply means it turns the fan on a preset time after the thermostat makes the connection to the furnace calling for heat.

A TDR will turn on regardless of whether the burners lite or not. The tdr remains active for several minutes after the thermostat disconnects from the heater. It a Time activated switch.

Regards & Good Luck, Forum Host & Multiple Topic Moderator.
TCB4U2B2B Company Enterprises. Energy Conservation Consultant & Gas Appliance Diagnostics Technician.
 
 

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