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Old 10-28-2008, 06:40 PM   #1
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False Flame Sensor

I bought my house in March of 08 and had furnace issues form the get go. Prior to closing, an engineer had advised us the vestibule cover was cracked. This led to the seller replacing the heat exchange at our request. Since then I have had THREE different different companies out to have a look.(one who replaced the heat exchange, one who my home warranty company sent, and finally one that I just called on my own)..all come up w/ nothing. Here are the symptoms:

When turned on the fan seems to blow neutral/cold air almost constantly, unless I completely power the unit down. It even did this into the warmer spring months when the thermostat was set inthe 50's. This led me to turn the unit off for the summer, which leaves me where I am at now

It seems that only when I make a drastic change in the temperature requested at the thermostat ( say from 62 to 70 ) does the heat come on.

When I look at the unit as its simply blowing cold air and no heat the LED flashes 5 times, which according to the troubleshooting tips on the furnace tells me false flame sensor. One of the repairman noted this and replaced the flame sensor, however the trouble persisted.

Another suggested the thermostat being the source of the issue due to the blower coming on when heat isnt called for.

I don't intend to repair this on my own, furnace issues are beyond my scope of home repiar. However before I call over another repairman or buy a new thermostat I'm looking for some further insight...Any thoughts?


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Old 10-29-2008, 04:32 AM   #2
oops, did I do that!
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Does the furnace have a ground wire connected to the grounding lug in the furnace, and connected to the ground strip in your breaker panel?

Has the polarity of the power supply to the furnace been checked?

Has the ignition module been replaced? Furnace model and serial number would help, maybe a picture.


Last edited by 8 Ball; 10-29-2008 at 04:35 AM.
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Old 10-29-2008, 08:28 AM   #3
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Any idea what other things have been checked? How often will it not heat? A good tech should be able to test and bypass a number of items in your heating system to give a pretty definitive answer on what is the problem. I'm a little surprised that hasn't happened so far. Maybe its time to call one of these guys back or find someone new.
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Old 10-30-2008, 11:00 AM   #4
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Thanks for the reponses...I should be able to get a picture and some other info when I get home tonight.

The first tech that came out replaced the flame sensor..I believe I neglected to mention that in my initial post. Would that be the same as or part of the ignition module? I do not believe the polarity has been looked at.

The furnace keeps the house warm but the fan is almost constantly running. I havent found a definitive pattern of when it actually blows heat.
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